题目

一圆锥的侧面展开图是半径为的半圆，则该圆锥表面积为（ ）A. B. C. D. 答案：【答案】A【解析】设底面圆的半径为r,则所以r=2,再求圆锥的表面积.设底面圆的半径为r,则，所以圆锥的表面积为.故选：AWe talk every day. When we have good news, we like to share it with our good friends and when something terrible happens, we make it known to others soon. But can you imagine that a tree can talk and share hews too? Of course, no tree moves lips and says words just as people do. Strange as it may sound, though, some trees do manage to communicate with each other.Willow(柳树) trees are the best-known of these trees. When insects(昆虫) begin nibbling(叮咬) a willow tree, the tree sends out a special smell at once. This smell tells the other willows that harmful insects are coming near. All of them quickly make a chemical(化学物质) in their leaves. This chemical is bad to the insects. The insects do not like it and they fly away soon. In this way, the willow trees protect themselves from the insects.The next time when you take a walk in the woods, maybe the trees are “talking” to each other quietly. And when someone says that trees cannot “talk”, please tell them that even trees give messages to each other, too.【小题1】Willow trees send messages with _________.A．wordsB．movementsC．smellsD．sounds【小题2】the underlined word “lips” in the first paragraph means ________.A．树干B．嘴唇C．枝条D．手势【小题3】 The passage tells us that some of the trees can ________.A．speak just as people doB．tell stories to othersC．communicate with each otherD．kill insects in the woods【小题4】According to the passage, the right order of the following is ________.a. The willow tree gives out a smell.b. The willow trees make a chemical in their leaves.c. Insects fly a way because of the chemical.d. Insects begin nibbling a willow tree.A．d-a-b-cB．d-b-a-cC．a-b-c-dD．d-c-b-a