哺乳动物神经细胞间信息传递主要靠（）
A.单纯扩散
B.化学突触
C.电突触
D.易化扩散
E.非突触性化学传递
参考答案：B
His letter, _____ to the wrong number, reached me late. [ ]
A. having been addressed
B. to have addressed
C. to have been addressed
D. being addressed
number of visitors came but I don’t know number．
A．A ; the
B．The ; a
C．A ; a
D．The ; the
