比较大小:3+7+5○18-5-2。
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. To save class time, our teacher has ___ students do half of the exercises in class and complete the other half for our homework.
A.us
B.we
C.our
D.ours
代表心室除极和复极总时间的是()
A.P波
B.QRS波群
C.S-T段
D.T波
E.Q-T间期