What Can We Conclude About the Relationship Between a Person's

What can we conclude about the relationship between a person's age of acquisition of a second language and his or her mastery of grammar?

A) So far,no research has demonstrated a relationship between these two variables.
B) Linguistically skilled individuals tend to master grammar better if they learn a second language during childhood; individuals with below-average skills tend to master grammar better if they learn a second language during adulthood.
C) The results clearly support the critical period hypothesis,because people have greater mastery of grammar if they learn a second language during childhood.
D) The results are complicated,because the answer depends on the match between the two languages,as well as the amount of education in the second language.