Passenger pigeons (旅鸽) were the most common birds in all of North America in the 1800s. It was common to see large groups of passenger pigeons — groups that made a sound like a storm. But today, they are extinct because of human behavior. Now, some scientists want to bring passenger pigeons back to life by using new technology and scientific ideas. They call this process de­extinction.

    De­extinction has not happened yet. It is still just an idea. The process of de­extinction is not easy. First, scientists must collect DNA from the bodies of extinct animals. Then they will put it in the eggs of similar animal species. When these animals become adults, they will have babies. And these baby animals will have the DNA of the extinct animals.

    Scientists believe it is possible to bring back passenger pigeons and many other animals. However, not everyone thinks this is a good idea.

    Stuart Primm is the world's leading expert on modern animal extinction. He believes that bringing extinct animals back to life is bad for the earth. On one hand, these animals no longer have a safe place to live. On the other hand, they could cause other animals to die.

    Many other scientists do not agree with Stuart Primm. Stuart Brand, a writer and scientist, is one of them. He believes de­extinction is good for many reasons.

    "The current generation (当代) of children will experience the return of some unusual animals in their lifetime. It may be part of what defines their generation and their attitude to the natural world. They will take their parents to zoos to see the growing populations of passenger pigeons, and maybe even dodo birds. This will provide a good deal of money for zoos busy with extinct species restoration (恢复). Humans killed off a lot of species over the last 10,000 years. So, it's right to bring some back to life," he said.

    One night in April, Corey Simmons got on the New York City subway, heading from Manhattan to Brooklyn to pick up his son from his grandmother. Simmons knew he needed to open the green folder (文件夹) on his legs, because inside lay his son's math worksheets that father and son were supposed to complete together.

    His son, who was in third grade, had just failed a test on fractions (分数). Simmons, 40, was never great at math. He wasn't sure he remembered much about fractions. He opened the folder and started on a problem, but wasn't sure if he was doing it correctly.

    Just then, a man got on the train and sat next to him.

    "He looked like a professor or something," Simmons said. "He looked kind of smart... like he knew something about math."

    Like most New Yorkers, Simmons did not often talk to other people on the subway. This time, he shared his problem with the stranger. To his surprise, the man offered to help.

    The two men worked through the math problems. The stranger helped Simmons understand how to do the math, so he could later teach his son.

    The moment was captured (捕获) by Denise Wilson, who was heading home from her job and saw the pair doing homework. She posted the photo on Facebook. "I really love seeing things like this especially in New York," she wrote. "To be a dad... and put his pride aside and learn from a complete stranger... it was so cool."

    Simmons said he wasn't afraid to ask for help so he could help his son. "You have to ask questions to get information. I'm not shy to ask," he said. "I was letting him know 'I need help, you know, your assistance would be great here on the train.'"

    The 20­minute subway lesson gave Simmons high hopes that his son would pass the next test. "He's going to knock it out of the park," Simmons said.

    Do you remember the last time you spoke to your mother? And do you remember the last time you 1 how much you love her?

    I 2 say the most used three words "I Love You" to my parents because saying that to them face to face always makes me 3. However, the situation 4 the moment I learned about my mother's 5. In November 2016, it was confirmed (证实) that my mother had stage 3 breast cancer. I knew there was little 6 of beating this illness.

    However, we didn't stop. We 7 all her doctor's advice. She 8 the process of the chemical treatment. But the cancer isn't 9 to beat. It took all of my mother's will and desire to get well.

    For two years, she continued to 10 against the disease. All through her journey, different people were there to 11 her in any way they could — financially, mentally, and even materially. I've seen 12 these people became part of her life. Whenever my mom 13 giving up, they would try to uplift her spiritually. I'm really 14 for their generosity.

    A few days ago, my mother lost her 15. Her body had given up and became 16. It wasn't easy to accept the fact. But I know it wasn't too late to 17 all the things a mother had done to her 18. Most of us can't notice their love until they aren't around us anymore.

    I will 19 my mom forever. It has only been less than nine days since she left us, 20 I'm sure that she knows my feelings all the time.

    Working with elephants is one of the most popular volunteer activities in Thailand. And for good reason, these (amaze) creatures are huge, cute, and very intelligent. Often elephants (look) on as gentle animals, but it's good to remember that this isn't always the case. (sad), many elephants have faced terrible treatment, beaten into (give) performances or overworked at money­hungry tourist attractions. A terribly­treated elephant can become angry and kill if it feels threatened.

    All that being said, volunteering for elephant (protect) can be a very rewarding experience. The important thing is to find the right opportunity. There are number of elephant sanctuaries (动物保护区) and parks, especially in Thailand. There you can do meaningful work (improve) the lives of elephants. The key is to do your research and watch out for places promise you big money.

If the volunteer organization seems to be paying more attention elephant rides and the elephants giving performances, be careful it is probably not a place with the elephants' best interests in mind.