请帮忙解释一道充分必要题

adasuying2004

Dears，对于充分必要我总是非常confused。特别是这道题。提请亲们帮帮忙啊帮帮忙~
Teachers are effective only when they help their students become independent learners. Yet not until teachers have the power to make decisions in their own classrooms can they enable their students to make their own decisions. Students’ capability to make their own decisions is essential to their becoming independent learners. Therefore, if teachers are to be effective, they must have the power to make decisions in their own classrooms.
According to the argument, each of the following could be true of teachers who have enabled their students to make their own decisions EXCEPT:
(A) Their students have not become independent learners.
(B) They are not effective teachers.
(C) They are effective teachers.
(D) They have the power to make decisions in their own classrooms.
(E) They do not have the power to make decisions.
答案是E。