某演唱会检票前若干分钟就有观众开始排队等候入场，而每分钟来的观众人数一样多。从开始检票到等候队伍消失，若同时开4个人场口需50分钟，若同时开6个人场口则需30分钟。问如果同时开7个入场口需几分钟 ()
A．18分钟
B．20分钟
C．22分钟
D．25分钟
参考答案：D
解析： 根据题意可知，不变量是开始检票前就已经有的观众的人数。可设每分钟来的观众人数一样多，人数为X，同时开7个入场口需y分钟，列算是为：(4-X)×50=(6-X)×30=(7一X)×y，当每分钟来一位观众检票时，即X=1时，y=25。故选D。
用方框中所给单词的适当形式填空，使短文通顺、正确、连贯。
down. Just then a poor man, Robert, came. He was on his way back home from work as __1__. The lady thought, "Is the man going to help me? He looks very cold and hungry." But to her surprise, he stopped and said __2__ a smile, "What's wrong, madam?" The lady told him what was happening. After forty minutes, the car was at last fixed by Robert. The lady wanted to pay him. "No, that's __3__, madam." he said, "I was just helping someone in need. If you really want to pay me back, I hope __4__ you see someone in trouble, you can give him a hand." A few minutes later, the lady saw a shabby (破旧的) house by the road. She __5__ Robert's words, so she stopped. The hostess (女主人) warmly asked her in. The lady could see that was not a __6__ family and they needed help. When the hostess was making tea in the kitchen, the lady __7__ 500 dollars on the table and went away quietly. Robert came home later than before, thinking how hard their life was. Their __8__ was to be born the next month but there wasn't __9__ money. His wife went up to him, gave him a kiss and said softly, "Don't worry, dear! Everything's going to be all right. A stranger has helped us out." Let's always be ready to help others because helping others is helping __10__. |