题目

如图在四面体ABCD中，若截面PQMN是正方形，则在下列命题中正确的有______填上所有正确命题的序号，，截面PQMN，异面直线PM与BD所成的角为． 答案：【答案】【解析】由截面是正方形出发，利用线面平行的判定和性质，可以推出，,从而得到平面,异面直线与所成的角和与所成角相等为，，不一定是中点从而不一定相等。解：在四面体中，截面是正方形，，平面，平面，平面．平面平面，，可得平面．同理可得平面，．，．由，是异面直线与所成的One day a mime(哑剧演员) is visiting the zoo and tries to earn some money as a street performer. As soon as he starts to draw a crowd, a zookeeper pulls him into his office. The zookeeper explains that the zoo’s most popular attraction, a gorilla(大猩猩), has died suddenly and the keeper fears that attendance(出席人数) at the zoo will fall off. He offers the mime a job to dress up as the gorilla. The mime accepts.The next morning the mime puts on the gorilla suit and enters the cage before the crowd comes. He soon discovers he can sleep, play and make fun of people and he draws bigger crowds than he ever did as a mime — the job he likes but loses.However, with days going by, he begins to notice that the people are paying more attention to the lion in the cage next to his. Not wanting to lose the attention of his audience, he climbs to the top of his cage, crawls across a partition(隔墙), and dangles(悬挂) from the top to the lion’s cage. The lion gets angry at this. The scene is a fuel to the crowd.At the end of the day he is given a raise for being such a good attraction — well, this continues for some time. The crowds grow larger, and the mime’s pay keeps going up.Then one day when he is dangling over the lion he slides and falls. The mime is terrified. He starts screaming “Help me!”, but the lion is quick. The mime soon finds himself flat on his back looking up at the angry lion and the lion says, “Shut up you fool! Do you want to get us both fired?”1.The mime accepts the zookeeper’s offer because __________.A. he has been out of workB. he doesn’t like being a mimeC. he likes performing at the zooD. he is offered a higher pay there2.How does the mime find the job dressing up as the gorilla?A. Hard and tiring. B. Dangerous but exciting.C. Easy and funny. D. Boring but well-paid.3.The mime’s first contact with the lion is to __________.A. find pleasure for himself B. get the lion’s attentionC. get his pay raised D. win back his audience4.The underlined words “a fuel” in Paragraph 3 can be replaced by __________.A. frightening B. disappointingC. exciting D. Familiar