A.f（x）=-a                                     B.f（x）=-a

C.f（x）=|a|                                    D.f（x）=a

A.（）^x=0                                     B.10^x=0

C.（）^x=0                                    D.2^x=0

A.4                      B.-2                        C.1                     D.0

A.充分不必要条件                                     B.必要不充分条件

C.充要条件                                              D.既不必要也不充分条件

（1）y=；（2）y=.

（1）y=（0.99）^x；

（2）y=；

（3）y=x^-3+1.