重度有机磷中毒时，全血胆碱醋酶活力应为（）
A.70%以下
B.60%以下
C.50%以下
D.40%以下
E.30%以下
参考答案：E
—Did your grandma like dancing when she was young?
—_______[ ]
A. Yes, she did.
B. Yes, she does.
C. No, she don't.
D. No, she isn't.
使用任何仪器进行测量时，都存在测量误差。
