一质点做简谐运动，则下列说法中正确的是( ) A．若位移为负值，则速度一定为正值

根据《建筑物防雷设计规范》规定，防雷接地装置的冲击接地电阻不应大于( )n。

A．10

B．20

C．30

D．50

已知函数f（x）=x+x³，x₁，x₂，x₃∈R，x₁+x₂＜0，x₂+x₃＜0，x₃+x₁＜0，那么f（x₁）+f（x₂）+f（x₃）的值（　　）

A．一定大于0

B．一定小于0

C．等于0

D．正负都有可能

从巴比妥药物的pKa值判断，哪个药物显效最快

A．苯巴比妥，pKa值为7.4(未解离率50%)

B．异戊巴比妥，pKa值为7.9(未解离率75%)

C．戊巴比妥，pKa值为8.0(未解离率80%)

D．司可巴比妥，pKa值为7.7(未解离率66%)

E．海索巴比妥，pKa值为8.4(未解离率90%)

1. I could hardly keep from _____(laugh) when he slipped and fell.

2. I'd like to see you _____(come) back soon.

3. I hope you can stop _____(play) the computer games during the school.

4. I saw that Nancy kept her seat,without hardly _____( move)at all.

5. A few other good things would _____(come)to the table on the first call.

特种设备压力管道，其范围规定最高工作压力大于或者等于（）MPa（表压）的流体，且公称直径大于（）mm的管道。

A.0.2；25

B.0.1；25

C.0.2；20

D.0.1；20