题目

若为有理数），则                （    ） A．33                          B． 29                  C．23                          D．19 答案：B 解析:本题主要考查二项式定理及其展开式。属于基础知识、基本运算的考查。       ∵         ，        由已知，得，∴，故选B。After lunch, without permission from parents, the two boys set off to explore the part of the beach which lay beyond the headland(陆岬，伸出海面的尖形高地).They had persuaded their young sister to _1_, saying that the long walk would be too _2_for her. Once they had got in the head land, the beach reached away endlessly before them. It was like _3_a new world. There were damp, dark caves to _4_,there were many_5_ among the rocks, full of sea creatures(生物);and, here and there along the beach were those _6_ objects, washed up and _7_ by the tide.The afternoon passed _8_The sun was already _9_when the boys reluctantly(恋恋不舍地) _10_ to make their _11_ homewards. But long before they reached the headland, they could see that the tide had come in so sudden that they were now _12_from either end of the beach. Their only chance of _13_ was to find a way up the cliff(悬崖) nearby.They soon find a narrow path _14_ the cliff top. But half way up their path was_15_by a large rock which they could not climb_16_The two boys had to_17_ at the top of their voices, _18_ that someone might_19_over the top of the rock, and finally came their father with two policemen. _20_of them climbed down a rope which was lowered over the rock. The boys were then pulled to safety, and thus saved from spending a miserable night on the cliff.1. A. keep quiet    B. stay behind       C. take a rest        D. join them2. A. tiring        B. exciting          C. uninteresting     D. impossible3. A. discovering   B. facing           C. enjoying         D. imagining4. A. look up     B. explore           C. hide in          D. search5. A. lakes        B. rivers            C. waterfalls        D. pools6. A. dirty        B .light             C. strange           D. clean7. A. moved       B .covered          C. beaten           D. left8. A. quickly      B. unexpectedly      C. finally            D. suddenly9. A. leaving      B. dropping          C. going            D. setting10. A. forgot      B. decided           C. succeeded        D. turned11.A. road        B. way             C. track            D. path12. A. cut off      B. left behind         C. held back        D. put away13. A. running off  B. keeping clear       C. getting away      D. turning back14. A. reaching    B. passing            C. going up         D. leading to15. A. blocked     B. covered           C. stopped          D. filled16. A. on         B. over              C. round            D. through17. A. shout       B. shoot             C. repeat            D .renew18. A. wanting     B. guessing          C. believing          D. hoping19. A .turn        B. appear            C. hide              D. climb20. A. Any        B. None             C. One              D. First