问题
选择题
The smile on Mary's face shows that she is ____ her work.
[ ]
A. worried about
B. pleased with
C. sorry for
D. afraid of
答案
答案：B
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The smile on Mary's face shows that she is ____ her work.
[ ]
A. worried about
B. pleased with
C. sorry for
D. afraid of
答案：B
J；将该粒子从D点移动到C点，电场力做功为
J。则以下分析正确的是 
J
J
J，则此匀强电场的方向一定是从A点指向B点的方向
C，则A、B之间的电势差为1.5V