The results showed that the younger they started to learn, the better."Studying a language means you get an entrance to another world," explained the scientists.

21.The main subject talked about in this passage is 　　 　.　

A. science on learning a second language

B. man's ability of learning a second language

C. findings that language learning can help brain power　

D. language learning and maths study

22.The last sentence of the second paragraph is intended to 　　 　.

A. say language learning is also a kind of physical labor

B. prove that one needs more practice when he (she) is learning a language

C. show the importance of using it when you learn a language

D. make people believe language learning helps grey matter work well

23.We may know from the scientific findings that 　　　.　

A. the earlier you start to learn a second language, the higher the grey matter density is

B. there is no difference between a later second language learner and one who doesn't know a second language