题目内容：

    Learning a second language is tricky at any age. Now, in a new study, scientists have worked out the exact age at which your chances of reaching fluency in a second language seem to drop: 10.

The study, published in the journal Cognition, found that it's nearly impossible for language learners to reach native-level fluency if they start learning a second tongue after age 10. But that's not because language skills start to go downhill. "It turns out you're still learning fast, "says study co-author Joshua Hartshorne, an assistant professor of psychology at Boston College. "It's just that you run out of time, because your ability to learn starts dropping at around 17 or 18 years old. People who start a few years after age 10 may still become quite good at a language," the authors say, "but they are unlikely to become fluent." Kids may be better than adults at learning new languages for many reasons. Children's brains are more plastic than those of adults, meaning they're better able to adapt and respond to new information. "All learning involves the brain changing," Hartshorne says, "and children's brains seem to be a lot more skillful at changing. " Kids may also be more willing to try new things and to potentially look foolish in the process than adults are. Their comparatively new grasp on their native tongue may also be advantageous. Unlike adults, who tend to obey the rules and patterns of their first language, kids may be able to approach a new one with a blank page.

These findings might seem discouraging, but it was heartening for scientists to learn that  the critical(关键的) period for fluent language acquisition might be longer than previously thought. Some scientists believed that the window began to close shortly after birth, while others extended it to early adolescence. Compared with those estimates (评估), age 17 or 18 — when language-learning ability starts to drop off—may seem relatively old.

1.What is the best period to learn a second language?

A.Before ten. B.Early adolescence. C.Age fifteen. D.Age seventeen or eighteen.

2.When it comes to new things, what does the writer think of kids compared with adults?

A.They're less skillful. B.They're less interested.

C.They're more flexible. D.They're more stubborn.

3.What does the underlined word "window" in the last paragraph refer to?

A.Interest. B.Chance. C.Confidence. D.Motivation.

4.Which of the following can be the best title for the text?

A.It's Never Too late to Learn a Second Language.

B.It Takes Time to Be Good at a Second Language.

C.Do We Really Need to Learn Foreign Languages?

D.Why Kids Learn Languages More Easily than Adults.