( ) 1. What do you have for lunch? ( ) 2. Do you like apples? ( ) 3. What would you like for dinner? ( ) 4. What's your favourite fruit? ( ) 5. What do you do on Sundays?
A. I like apples. B. I often play football. C. Yes, I do. D. I have onions and tofu. E. I'd like some mutton.
，则激光在此均匀介质中的波长变为在真空中波长的______倍；某激光光源的发光功率为P，发射激光的波长为λ，该激光进入上述介质时由于反射，入射能量减少了10% ，该激光在这种介质中形成的光束横截面积为S，则在垂直于光束传播方向的截面内，单位时间内通过单位面积的光子个数为______。（已知普朗克常量为h）