问题
选择题
Freeze! Hands up ________ get out of your car! [ ]
A. or
B. to
C. but
D. and
答案
答案：D
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Freeze! Hands up ________ get out of your car! [ ]
A. or
B. to
C. but
D. and
答案：D
，当光由玻璃射向空气时，发生全反射的临界角为45°，一束光以与MN平面成45°角的方向射向半圆柱形玻璃，求能从MN射出的光束的宽度为多少？