下图中N为北极点，AB为晨昏线的一段，且B为晨昏线与某一纬线的切点，这一天B点最大太阳高度为40°，B、C在同一经线上。读图，完成下题。 A点位于（
甲、乙两物体都做匀速圆周运动，其质量之比为1∶2，转动半径之比为1∶2，在相等时间里甲转过60°，乙转过45°，则它们所受外力的合力之比为（
小丽同学在刚买来的袋装薯片中发现还有一个小袋，上面标有“成分：CaO、Fe;作用：防潮、防氧化；警告：禁止食用”等字样，撕开小袋，发现里面的
设数列{an}满足a1=2,an+1=2an+2,用数学归纳法证明an=4×2n-1-2的第二步中,设n=k时结论成立,即ak=4×2k-1-2,那么当n=k+1时, __________.
It was ______ creative thinking that I took the course, not to get high marks in exams. A. developing B. to develop C. developed D. to have developed
Living on Mars isn’t ________ as it sounds. A. as strange an idea B. as idea strange C. as a strange idea D. as an idea strange
We had a really bad time about six months ago but now things are . A. looking up B. coming up C. making up D. turning up
亚当•斯密说过：“如果一个社会的经济发展成果不能真正分流到大众手中，那么它在道义上将是不得人心的，并且有风险的，因为它注定会威胁到社
中，自变量x的取
值范围是 ▲ ． 
解析: