In students' eyes, a good teacher should have many good virtues, but _____, he or she should be knowledgeable. [ ]

A. above all

B. after all

C. first of all

D. in all

兴奋在神经细胞间传递是通过突触来传递的。下列对于递质的叙述，错误的是（）

A.递质通过突触前膜释放到突触间隙，作用于突触后膜

B.递质是一种化学信号

C.递质能使突触后膜电位发生改变

D.递质传递是双向的