4本不同的书放入两个不同的大抽屉中,共有不同的放法为( )
A.6种;
B.8种;
C.16种;
D.20种;
答案:C
每本书有两种选择,根据乘法原理,可知不同的放法有种选法.
At one point along an open highway,I came to a crossroads with a traffic light. I was alone on the road by now, but _小题1:__ I drove up to the light,it turned red,and I braked to a halt. I looked left, right,and behind me. Nothing,_小题2:__a car,no suggestion of headlights, but there I sat,_小题3:_(wait) the light to change,the only human being for at least a mile in any direction.
I started wondering _小题4:_I refused to run the light. I was not afraid of __小题5:_(catch) by the police, because there was obviously no cop anywhere around and _小题6:certainly would have been no danger in going __小题7:_ it.
Much later that night,the __小题8:_ question of why I’d stopped for that light came back to me. I think I stopped because it’s part of a contract(合同) we all have with each other. It’s not only the law, but it’s an agreement we have,and we trust each other to honor _小题9:__:We don’t go through red lights. Like most of us, I’m more ready to be stopped from doing something bad by the social agreement that disapproves of it __小题10:_ by any law against it.
美国内战是一场 [ ]
A、资产阶级革命
B、无产阶级革命
C、社会主义革命
D、消灭奴隶制度的革命