激素的第二信使不包括（）
A.PIP2
B.cAMP
C.DG
D.Ca2+
E.IP3
参考答案：A
指标是说明总体特征的，而标志是说明总体单位特征的。（）
Mrs. Weng came back from France in 2010. She _______ there for four years. [ ]
A. works
B. worked
C. has worked
