天平未调水平,测量结果可能会出现 误差,电桥检流计的零点漂移会引起测量结果的 误差

用直流测温电桥来测量温度计电阻时，经常会发展检流计的零位有漂移现象，主要是由（）造成的。

A.温度计引线太长

B.电源稳定度差

C.温度计引线之间存在着杂散热电势

D.流过温度计的工作电流太大

使用单臂电桥测量直流电阻时在选择适当倍率后的操作内容如下，(1)测量前先将检流计锁扣打开，并调整指针在零点。(2)读取数字后，应先断开检流计按键，再断开电源按键。(3)反复调节检臂电阻，使之达到平衡后读出检臂电阻读数。4)测量时先接通电源按键，后接通检流计按键请指出操作步骤正确排列顺序是：()。

A、⑴⑵⑶⑷

B、⑴⑶⑵⑷

C、⑷⑴⑶⑵

D、⑴⑷⑶⑵

听力原文：W: Do you know if the bus station has time tables for buses to London M: I’m afra听力原文：W: Do you know if the bus station has time tables for buses to London M: I’m afraid they may not, but I know you can catch a bus to London that leaves everyday at 8:00 a. m. Q: What does the man want to know （）

A．Where the bus station is．

B．If he can catch a bus that leaves for London．

C．If he’ll have time to catch the bus．

D．When buses leave for London．

听力原文：M: Do you know if the bus sttion hs timetbles for buses to Chicgo W: They my听力原文：M: Do you know if the bus sttion hs timetbles for buses to Chicgo W: They my not, but I know you cn ctch bus to Chicgo. Wht does the mn wnt to know If he’ll hve time to et in Chicgo. B．Where the bus sttion is locted. C．When buses deprt for Chicgo. D．If he cn ctch bus tht leves Chicgo.

A．If he’ll have time to eat in Chicago．

B．Where the bus station is locateD

C．When buses depart for Chicago．

D．If he can catch a bus that leaves Chicago．

A．attempts

B．requests

C．doubts

D．promises