下列表达式中正确的是()。
A.
B.
C.
D.
参考答案:A
Many funny stories written by Andersen make us _____.[ ]
A. to laugh
B. laughing
C. laugh
核磁共振氢谱中,化学位移值的范围是()
A.51~60
B.41~50
C.31~40
D.21~30
E.0~20