A.2^b>2^a>2^c                   B.2^a>2^b>2^c

C.2^c>2^b>2^a                   D.2^c>2^a>2^b

A.2                B.2                C.-2               D.-2

A.(0,)                                     B.(0, ］

C.( ,+∞)                                D.(0,+∞)

A.R                                            B.［8,+∞)

C.(-∞,-3］                                 D.［-3,+∞)

A.A={1,2,4,8,16}

B.A={0,1,2,log23}

C.A{0,1,2,log23}

D.不存在满足条件的集合

(1)证明函数f(x)在(-1,+∞)上为增函数;

(2)用反证法证明方程f(x)=0没有负数根.

(2)化简:.