一束光线从空气射入水中,入射角为40°,在界面上光的一部分被反射,另一部分被折射,则反射光线和折射光线之间的夹角θ是 A.100°<θ<140° B.θ>140° C.θ<50° D.50°<θ<100° 答案:A 解析:如图∠AON=40°,由反射定律知∠BON=40°,由折射定律知∠CON′<40°,所以100°<∠BOC<140° .
The river is very long and it is about ________.
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A.20 metres wide
B.15 metres long
C.30 metres high
D.50 metres tall