Theresa Began Studying Japanese When She Was in the Eighth

Theresa began studying Japanese when she was in the eighth grade. After many years of study, however, she still speaks Japanese with an accent and lacks perfect fluency. This is probably because

A) she had already passed the critical period of language development when she began studying Japanese.
B) she was not genetically "prewired" for Japanese.
C) no one can learn to speak a language perfectly unless their parents speak it.
D) continuing to speak English while she was studying Japanese blocked her acquisition of Japanese.