As we all know, it is ____responsibility as well as ___honor for a country to be chosen to host the Olympic Games.

A．a, a

B．the, the

C．a, an

D．an, an

生物变异的方向是

A．一定对生物后代个体有利

B．一定对生物后代个体不利

C．变异通常对生物个体没有影响

D．变异使生物产生各种不同类型