一束光射到平面镜上,入射角是30°,则反射角是 ______度,反射光线与入射光线的夹角是 ______ 度;如果这束光垂直射到平面镜上,这时入射角是____ 度.
30;60;0
Do you think 3,000 yuan is enough to ______ his needs for the tour to Beijing?
A.cost
B.cover
C.take
D.save
抽油机井和捞油井的密封填料盒都具有()作用。
A、防垢
B、输油
C、密封
D、连接