下列大环内酯类抗菌药物，对肺炎支原体作用最强的是（）
A.红霉素
B.吉他霉素
C.罗红霉素
D.阿奇霉素
E.交沙霉素
参考答案：D
I have been living in the United States for twenty years,but seldom _______ so lonely as now.
A．have I felt
B．I had felt
C．I have felt
D．had I felt
如图所示的事例中，属于运用了重力方向的是 [ ]
检查相框是否挂正
用力拉弹簧
往墙上敲钉子
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