预防医学是研究环境因素与
A．人体内环境的关系B．人体外环境的关系C．人体健康的关系D．人体状况的关系E．人体功能的关系
参考答案：C
More and more old people are skiing but it has ______ to do with snow and slopes: this type of skiing stands for Spending the Kids Inheritance.
A．something
B．nothing
C．everything
D．anything
设函数f（x）=lntanx，则f'（x）=（）。
A.2cscx
B.2csc2x
C.
D.cotx
