命题“若a＞b，则2^a＞2^b”的否命题为(      )

A．若a＞b，则有2^a≤2^b．

B．若a≤b，则有2^a≤2^b．

C．若a≤b，则有2^a＞2^b．

D．若2^a≤2^b，则有a≤b．

all the required papers, he didn’t answer the questions fluently in class．

A．Having not read

B．Not having read

C．Not read

D．Not to read