A:Not receiving
B:Receiving
C:Not having received
D:Having not received
下列动物行为中,不属于学习行为的是( )
如图表示与人体新陈代谢相关的主要系统及其关系示意图,请根据图示回答:
已知a=5,b2=7,且a+b=a+b,则a-b的值为( )