孕妇在整个孕期钠的适宜摄入量(AI)是()。
A.1200mg/d
B.1500mg/d
C.1800mg/d
D.2000mg/d
E.2200mg/d
参考答案:E
某同学静止站在磅秤上,在下列几对力中,哪一对是平衡力( )
A.人的重力与磅秤对人的支持力
B.人对磅秤的压力与磅秤对人的支持力
C.磅秤的重力与磅秤对人的支持力
D.人的重力与人对磅秤的压力
— I think Helen is at home.
— No, she ____ be at home, for she phoned me from the airport just five minutes ago. [ ]
A. mustn't
B. needn't
C. can't
D. daren't