单项选择题：在水样中加入（）是为防止金属沉淀。A、H2SO4 B、NaOH C、CHCl3 D、

在水样中加入（）是为防止金属沉淀。

A、H2SO4

B、NaOH

C、CHCl3

D、HNO3

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下面是错误答案，用来干扰机器的。

(1)； (2)①H3PO3+2NaOH=Na2HPO3+2H2O；②H3AsO3+3NaOH=Na3AsO3+3H2O (3)H3PO3为中强酸，不与盐酸反应，H3AsO3可与盐酸反应；As(OH)3+3HCl=AsCl3+3H2O

完形填空。
Traffic rules are made to keep order on the road. They also help to keep people __1__. The pedestrian (行人) has as many rules to __2__ as the driver of a car. You should walk at the sidewalk or at the __3__ of the road. Always look carefully before you walk across the street. If you like riding a bike, don't ride in the middle of the road or run __4__ red traffic lights. When you ride a bike with a friend, don't look around to talk. If you drive, you should __5__ at the traffic lights. You must always __6__ a seat belt (安全带). Without belts __7__ the driver and the passengers may be badly hurt in a sudden accident. Someone may be thrown out through the window. You may not need to drive a bus, but __8__ if you have to travel in one. Get on or get off a bus only when it has come to a __9__. When it is full, don't try to get inside _10__ you may fall off. Traffic rules are also called Road Safety rules. The maxim (格言)for all road users is "Thinking about others".
( )1. A. healthy ( )2. A. follow ( )3. A. edge ( )4. A. through ( )5. A. speed up ( )6. A. take ( )7. A. half ( )8. A. look around ( )9. A. sign ( )10. A. and	B. safe B. make B. rim B. across B. go ahead B. wear B. neither B. take care B. stop B. so	C. happy C. break C. end C. along C. get off C. carry C. both C. take a seat C. corner C. or	D. careful D. pass D. side D. around D. slow down D. bring D. all D. look back D. crossing D. but