Carl looks sad these days,but we don't know________is bothering him.
A:what is it
B:what it is
C:what is it that
D:what it is that
下列关于生物与环境关系的叙述正确的是( )
—Give ____ (I,me) an orange , please.
—Here ____ ( you, your) are.
设a=log54,b= (log53)2,c=log45,则( )