问题
选择题
用手握住酒瓶，使其口朝上底朝下竖直静止在手中，对此下列说法中正确的是 [ ]
A．酒瓶能静止在手中，是由于手对酒瓶的握力等于酒瓶的重力
B．酒瓶能静止在手中，是由于酒瓶受到手对它的摩擦力的作用
C．手握酒瓶的力增大，瓶子所受摩擦力也随着增大
D．向酒瓶注水的过程中，即使手握瓶的力不变，瓶所受的摩擦力也将增大
答案
答案：B
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用手握住酒瓶，使其口朝上底朝下竖直静止在手中，对此下列说法中正确的是 [ ]
A．酒瓶能静止在手中，是由于手对酒瓶的握力等于酒瓶的重力
B．酒瓶能静止在手中，是由于酒瓶受到手对它的摩擦力的作用
C．手握酒瓶的力增大，瓶子所受摩擦力也随着增大
D．向酒瓶注水的过程中，即使手握瓶的力不变，瓶所受的摩擦力也将增大
答案：B
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| Life today has brought new problems. One of 1 problems is pollution. Water pollution 2 our rivers and lakes dirty. It kills our fish and polluted our 3 water. Noise pollution makes us 4 louder and become angry more easily. Air pollution is the most serious kind of pollution. It's bad for all 5 things in the world. Cars, planes and factories all pollute our air every day. Sometimes the polluted air is 6 it is like a quilt over a city. This kind of quilt is 7 smog (烟雾). Many countries are making rules to fight pollution. Factories must now clean their water before it is thrown away, and they mustn't blow dirty smoke into the air. We need to do many other things. We can put waste things in the dustbin and not throw it on the ground. We can go to work by bike or with our friends in the same car. If there are 8 people driving, there will be less pollution. Rules are not 9 . Every 10 must help fight pollution. | ||||
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