—There goes the bell.

—It' s time for class. Let' s stop _______. [ ]

A. talk

B. to talk

C. talking

D. not talk

下述生理活动，不属条件反射的是

A．膀胱贮尿过多，导致排尿
B．闻到食物香味，导致唾液分泌
C．天气炎热导致出汗
D．肾上腺素分泌过多，使心跳加快