第二次世界大战的转折点是[ ]
A．莫斯科保卫战
B．华沙之战
C．不列颠之战
D．新大林格勒战役
答案：D
Coming into the room, I found them ______ at the table, _____ chess. [ ]
A. seated; playing
B. seating; playing
C. seat; play
D. seated; played
力矩的概念是什么
