通过学习内能、热机的内容，可知：  　  [     ]

A． 物体运动的动能和所有分子势能的总和，叫做物体的内能　

B． 改变物体内能的方式有两种：做功和热传递　

C． 在热机的一个工作循环中，燃气做功四次　

D． 在做功冲程中，是机械能转化为内能

William Sidney Porter, known as O. Henry, is most famous for ______.

A. his poems


B. his plays
C. his short stories


D. his novels