简述孔径光阑确定方法。
参考答案：
将系统的所有光阑通过其前面的光学零件成像到物空间，其孔径对物面中心点张角最小的像所对应的光阑即为系统的孔径光阑。
The farm as well as its neighboring hills we once spent so much time ___ a new look recently.
A．on has taken
B．has taken
C．on having taking
D．having taken
Why not listen to music? It can make you relaxed.
A. How about B. Let’s C. Why don’t you
