如图甲所示，在平静的水面下有一个点光源s，它发出的是两种不同颜色的a光和b光，在水面上形成了一个被照亮的圆形区域，该区域的中间为由ab两种单色光所构成的复色光的圆形区域，周边为环状区域，且为a光的颜色（见图乙）。则以下说法中正确的是
A、a光在水中的传播速度比b光大
B、水对a光的折射率比b光大
C、a光的频率比b光大
D、在同一装置的杨氏双缝干涉实验中，a光的干涉条纹比b光窄
答案：A
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| I returned to Abuja, the capital of Nigeria, after graduation.I had been there before my mother became a minister. Two weeks later, I told my mother I was bored.She said, "Here're the car keys. Go and buy some fruit." 1 I jumped into the car and speeded off. Seeing me or rather my 2 , a boy sprang up (跳起来), 3 to sell his bananas and peanuts."Banana 300 naira.Peanut 200 naira!" Looking at his blackstriped bananas, I 4 to 200 total for the fruit and nuts.He 5 . I handed him a 500 naira note. He didn't have 6 , so I told him not to worry. He was 7 and smiled a row of perfect teeth. When, two weeks later, I 8 this same boy, I was more aware of my position in Nigerian society. I should 9 this country as the son of a 10 . But it was hard to find pleasure in a place where it was so 11 to see a little boy who should have been in school selling fruit. "What's up?" I asked. He answered in 12 English, "I...I no get money to buy book." I took out two 500 naira notes. He looked around 13 before sticking his hand into the car 14 the bills. One thousand naira means a lot to a family that 15 only 50,000 each year. The next morning, security officers told me, "In this place, when you give a little, people think you're a fountain of opportunity (机会)." 16 it's right, but this happens everywhere in the world.I wondered if my little friend had actually used the money for 17 . After six months' work in northern Nigeria, I returned and saw him again standing on the road. "Are you in school now?" He nodded. A silence fell as we looked at each other, then I 18 what he wanted.I held out a 500 naira note."Take this." He shook his head fiercely and stepped back 19 hurt. "It's a gift," I said.Shaking his head again, he handed me a basket of bananas and peanuts."I've been waiting to 20 these to you." | |||
| ( )1．A.Encouraged ( )2．A.car ( )3．A.willing ( )4．A.got down ( )5．A.explained ( )6．A.change ( )7．A.troubled ( )8．A.ran after ( )9．A.protect ( )10．A.minister ( )11．A.lucky ( )12．A.old ( )13．A.proudly ( )14．A.for ( )15．A.spends ( )16．A.Possibly ( )17．A.joys ( )18．A.asked ( )19．A.when ( )20．A.send | B．Disappointed B．mother B．afraid B．bargained down B．promised B．notes B．regretful B．ran into B．enjoy B．headmaster B．amazing B．broken B．madly B．with B．pays B．Actually B．nuts B．imagined B．as if B．provide | C．Delighted C．driver C．eager C．put down C．agreed C．checks C．comfortable C．ran over C．help C．manager C．funny C．traditional C．curiously C．at C．makes C．Certainly C．books C．reminded C．even if C．sell | D．Confused D．keys D．ashamed D．took down D．admitted D．bills D．grateful D．ran to D．support D．president D．common D．modern D．nervously D．upon D．affords D．Fortunately D．bananas D．realised D．after D．give |