— May I speak to Jim Green?
— _________ He is in the supermarket now.
A:Who are you speaking?
B:Yes, of course you can.
C:Could you call him later?
D:This is Jim Green.
图甲是某草原生态系统中几种生物之间的食物关系示意图,图乙是该生态系统的碳循环示意图,图中A,B,C,D表示生态系统的相关组成成分。