汽车在平直公路上匀速行驶，图中所示的四个图象中，能正确表示汽车速度与时间关系的是

Dear Lily,

I got your letter and pleased to hear about your job interview at a grocery store. I know you want to get a job at the TV station, and you’ve been looking for several week now and haven’t found something. The job at the grocery store doesn’t sound badly. If I am you, I’d take it. If you worked there for some time, you could earn some money. Its your decision, of course, but I advise you to take it. Let me to know what you decided to do. By the way, after you get the job you can think about get a bike later.

如图所示，一个与外界绝热的气缸有一个绝热的活塞，中间有一个固定的导热性能良好的隔板，封闭着两部分气体A和B，活塞处于静止平衡状态，现通过电热丝对气体A加热一段时间，后来活塞达到新的静止平衡状态，不计气体分子势能，不计活塞与气缸壁之间的摩擦，大气压强保持不变，则

A．气体A吸热，内能增加

B．气体B吸热，对外做功，内能不变

C．气体A分子单位时间内对器壁单位面积碰撞次数增多

D．气体B分子单位时间内对器壁单位面积碰撞次数不变

光源色温小于3300K时，称该光源为（）。

A.冷色光源

B.中性光源

C.暖色光源

D.冷色

二十世纪以来，最早将现代意义上的夜视器材投入实战的国家是（）。

A.德国和美国

B.前苏联

C.英国

D.日本

指出两种用渐变填充所选对象的方法？