When a survival craft drill is held，the person in charge must insure that（）.

A.all survival craft are lowered to the water，launched，and operated for thirty minutes

B.all davits used for launching liferafts are operated

C.each emergency position indicating radio beacon is tested for thirty minutes

D.the helicopter pad landing lights are operating in a quick-flashing mode

以低于中毒剂量的药物反复多次与生物接触一定时间后，体内某些部位化学物增加并储存，对机体产生的毒性作用称为（）

A.蓄积毒性

B.急性毒性

C.亚慢性毒性

D.慢性毒性