在有阳光的情况下，给你一张纸和一把刻度尺，如何粗略地测出凸透镜的焦距?
使凸透镜正对太阳，纸放在透镜后面，与透镜平行，并前后移动，直到在纸上出现一个最小最亮的光斑为止．量出这时纸与透镜 间的距离，就约等于凸透镜的焦距。
— At last, both of them died in the war.
一 Oh. that's touching.
10世纪初，统一契丹各部，916年建立契丹政权的少数民族首领是（ ）
Hello! I'm Ben. This is my new living room. It's quite big. There is a chair and two big sofas. There are some flowers beside the sofa. Between the sofas, there is a lovely cat. There aren't any pictures but a clock o n the wall. There is a computer on the desk next to the sofa. There is a TV set on the TV stand(电视柜) under the window. I often watch TV in my living room. What a nice living room.
① ____ ②____ ③____ ④ ____ ⑤ ____
