控制阀的开闭形式选择需要根据（）因素决定。

下列关于公积金个人住房贷款和商业银行自营性个人住房贷款的说法，正确的是( )。

A．前者的申请对象范围更广

B．前者贷款利率较高

C．后者是一种委托性个人住房贷款

D．后者的信贷风险由商业银行自身承担

在下列碳素结构钢中，强度较低，但有较好的塑性和韧性，易于冷加工的钢材牌号是( )。

A．Q215

B．Q235

C．Q255

D．Q275

Life gets noisier every day and very few people can be free from noise of some sort or another. It doesn’t matter where you live－ in the middle of a modern city, or a faraway village the chances that you will be disturbed by jet planes , transistor radios, oil-powered engines, etc, are almost everywhere. We seem to be getting used to noise, too. Some people feel quite lonely without background music while they are working.

Scientific tests have shown that total silence can be very frightening experience for human beings. However, some people enjoy listening to pop music which is very loud, and this can do harm to their eardrums (耳鼓). The noise level in some disco is far above the usual safety level for heavy industrial areas.

One recent report about noise and concentration(专心) suggested that although a lot of people say that any noise disturbs their concentration , what really affects their ability to concentrate is a change in the level of noise. It goes on to say that a background noise, which doesn’t change too much (music, for example ) may even help people to concentrate.

小题1:The best title for this passage is________.

A．Noisy Life

B．Background Noise

C．Disturbed Concentration

D．Changeable Noise小题2:From this passage, the pollution of noise __________.

A．doesn’t matter much

B．has become better in big cities

C．has become better in villages

D．has become worse everywhere小题3:Scientists have discovered that what prevents people from concentrating is _________.

A．any kind of noise

B．great changes in level of noise

C．background noise

D．various background music

PC机的运算速度是指它每秒钟所能执行的指令数目，提高运算速度的有效措施是 ( )。
①增加CPU寄存器的数目
②提高CPU的主频
③增加高速缓存(Cache)的容量
④扩充PC机磁盘存储器的容量

A．①和③

B．①、②和③

C．①和④

D．②、③和④

作废单证如何处理？