如图所示，一束白光从左侧射人肥皂薄膜，下列说法中正确的是（）

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问题选择题

①人从右侧向左看，可看到彩色条纹

②人从左侧向右看，可看到彩色条纹

③彩色条纹水平排列

④彩色条纹竖直排列

A．②③

B．①②④

C．②④

D．①③

答案

答案：A

白光从左侧射人肥皂薄膜，从膜的前后两面分别反射两列光为相干光，当当光程差为波长的整数倍时呈现亮条纹，当光程差为半个波长的奇数倍时呈现暗条纹．相同的高度肥皂膜的厚度相同，故出现水平的明暗相间的干涉条纹．

问答题

　　在不同语体和语言环境中，同一内容表达方式往往不同。请将“欢迎对方按时参加”的意思按限制条件表述，每句不得超过15个字。

①在商业广告中：_______________________________________________________

②在给兄弟单位的请柬中：_______________________________________________

③在给下级的通知中：___________________________________________________

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单项选择题

Should we care if over 150 known species of animals have (91) from the earth in the last fifty years Should we be concerned that there are (92) thousands of species whose very existence is (93) endangered—largely because of our activities (94) , after all, is the natural end of populations. Species are born, then (95) , and then die. Some live a (96) time, perhaps millions of years; some die more quickly. We have (97) the extinction of many species we know about, and we have undoubtedly sealed the (98) of others. In fact, there are undoubtedly many other species that have lived among us during our time on earth, but that have disappeared as a (n) (99) of our activities without our ever having known they existed.
It is hard to explain the rationale of many of us who are concerned about such matters. I have never seen a sea whale, (100) I don’t want them to become extinct. Moreover, I felt this way long before I understood anything about how they might be an important part of an ecosystem. Possibly such feelings merely reflect the cultural attitude that it is "nice" to wish other living things well; thus, the attitude is (101) . I feel nice.
There are, of course, more rational reasons for (102) the extermination of any species. For one thing, the kind of attitude that encourages or sanctions the destruction of other species is a threat (103) our own wellbeing. If such an attitude exists, we ourselves might (104) victim to it. living things (including us) might be expected to fare better where there is (105) for life. The extinction of other species could also threaten us (106) by simplifying the system of which we are a part or by destroying parts of the ecosystem (107) which we directly rely. For example, if we continue to poison the oceans (108) we are willing to believe only a few bottom dwellers are affected, we might (109) overstep some critical threshold and trigger the wholesale death of plankton, thus finding ourselves without a major (110) of the world’s food and with our oxygen supplies dwindling.

A．effect

B．result

C．issue

D．event

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