帮忙解释一道SAT语法改错题John believes that plants respond to human att

帮忙解释一道SAT语法改错题
John believes that plants respond to human attention,
which causes his talking to his African violets every
night.
(A) attention,which causes his talking
(B) attention and talking is what is done
(C) attention and his talks
(D) attention; for this reason has been his talking
(E) attention; he therefore talks
请问原句的错误在哪里?
那就是说在SAT里非限制定语中which一定不可以指代前面一个句子?