I'm very proud that Beijing is one of _______ cities in the world.
A:big
B:bigger
C:biggest
D:the biggest
①转动遮光器,使较大的光圈对准通光孔 ②转动转换器,使低倍物镜对准通光孔 ③左眼注视目镜,右眼睁开 ④转动反光镜调出一个白亮的视野
如图是元素周期表的一部分,请回答: