it is a dog, _ _?[ ]
A. doesn't it
B. is it
C. isn't it
答案：C
If you _____ your homework, you can go out to play football.
A. finish B. will finish C. are finishing
代表心室除极波形的是（）
A.P波
B.QRS波群
C.ST段
D.T波
E.QT间期
