—Shall we have a smoke here?
—No, we _____ because this is gas station and the worker is carrying some petrol.
A:can't
B:needn't
C:mustn't
D:won't
已知X、Y、Z三种元素组成的化合物是离子晶体,其晶胞如图所示,则下面表示该化合物的化学式正确的( )
如图是人体心脏结构示意图,请据图回答:
某种解热镇痛药的结构简式为
当它完全水解时,可得到的产物有( )