景深与焦长
参考答案：
在成一幅清晰像的前提下，像平面不变，景物沿光轴前后移动的距离称“景深”。景物不动，像平面沿光轴前后移动的距离称“焦长”。
—You will break down if you keep on doing like that.
—______, but I just want a good result in this exam. [ ]
A. Thanks a lot
B. Don’t mention it
C. You’re welcome
D. Sounds great
If cauliflowers are not ______ from extreme temperatures, the heads get discolored.
A．protected
B．shelter
C．shade
D．saved
