A:ever drank
B:was ever drinking
C:have ever drunk
D:had ever drunk
I’m glad to you. I know that you’ll come to see me from your letter and I feel very happy.
如图为某些微小生物的形态示意图,请据图回答下列问题:
动物对于一个生态系统来说是很重要的,这是因为( )