One of the best sources of evidence that there is a sensitive period for human language development is that
A) humans always develop language skills, no matter what linguistic environment they are in.
B) it can be very difficult for adults who are learning a second language to become proficient in the grammar of that language.
C) it is nearly impossible for children to master two languages before the age of ten.
D) the later one starts learning a language, the better he or she is at mastering the phonemes in the new language.

Question

Quizplus · Accepted Answer

The fact that adults often struggle to learn a second language proficiently suggests that there is a sensitive period for language development that ends in childhood. If this were not the case, adults would be able to learn languages as easily as children, which is not typically the case. Additionally, the fact that children are often able to learn multiple languages simultaneously (before the age of ten) suggests that there is a specific window of time during which language acquisition is particularly effective. Both of these observations support the idea of a sensitive period for language development.

One of the Best Sources of Evidence That There Is