雷达在搜寻目标时,接收到回波所用时间为1.2×10-4s,则此目标距雷达( )

题型:选择题

问题:

雷达在搜寻目标时,接收到回波所用时间为1.2×10-4s,则此目标距雷达(  )

A.36km

B.72km

C.18km

D.9km

考点:回声及回声测距离的应用
题型:选择题

采集蝴蝶标本在维多利亚女王时代的英国非常流行。英国大蓝蝶的标本很受欢迎,它不很大,也不很蓝,并不特别美丽,但数量稀少,且生活在人迹罕至的荒野。即便如此,仍然有大量的大蓝蝶被制作成标本。在19世纪末,已经开始有人呼吁保护它。进入汽车时代,到大蓝蝶栖息地更加方便,有的地方的大蓝蝶已经绝迹,保护更为迫切。1930年.英国建立了第一个大蓝蝶保护区。九年之后,保护区内的大蓝蝶种群灭绝了。此后,虽然保护区越来越多,但是大蓝蝶的数量越来越少。上世纪五十年代,英国大约还有数万只大蓝蝶,到1972年只剩下300多只。1975年,英国通过《野生动植物保护法》,首次把大蓝蝶列为法定保护对象,但已无济于事。1979年,英国最后一只大蓝蝶死去。这是为什么呢? 

每年六、七月间,是英国大蓝蝶飞翔的季节。大蓝蝶成虫的寿命只有四、五天,在短暂的生命结束前,雌大蓝蝶必须找到合适的百里香产卵。百里香必须是生长在红蚁巢的边上,而且含苞待放。卵被产在百里香的花蕾里。一两周后,大蓝蝶幼虫孵化出来,就以花为食,大约两周,在蜕了三次皮后,幼虫掉到了地上,等待红蚁。幼虫靠分泌蜜汁吸引红蚁。红蚁将其带回蚁巢,为了得到蜜汁,它会用触角拍打它。蜜汁分泌完时,幼虫就有生命危险,这时它会像红蚁幼虫那样蠕动,发出红蚁的气味和声音,让红蚁误以为它是蚁巢中的一员。 

大蓝蝶幼虫要在蚁巢中整整待上十个月,不仅能躲避天敌,还以红蚁的卵和幼虫为食。但是大蓝蝶幼虫仍然面临重重危险。红蚁蚁后会误以为它是一只以后也将变成蚁后的超级红蚁幼虫,而让工蚁杀死它;如果蚁巢规模太小,或者又来了另一只大蓝蝶幼虫,食物不够,最终也会饿死。 

但红蚁本身对生活环境也有要求:它们喜欢温暖,在朝南向阳的山坡筑巢,地面上草的高度最好只有2~3厘米,因为草太高会遮住阳光,蚁巢温度太低,红蚁幼虫会冻死。当大蓝蝶的栖息地被划为保护区后,禁止烧荒、放牧,野草疯长:本来还有野兔能在一定程度上抑制草的生长,但在上世纪50年代,一种传染性很强的病毒入侵英国,使野兔的数量锐减99%。草越长越高,大蓝蝶依赖的红蚁迅速消失,被另一种较耐寒的红蚁取而代之。这种红蚁也喜欢吃蜜汁,但它们能识破伪装,将大蓝蝶幼虫杀死。等到草皮高度超过10厘米,连百里香也难以生长、繁殖了,等人们发现这一奥秘,已经太迟了,英国大蓝蝶灭绝了。 

为了让大蓝蝶再次飞翔,英国逐渐恢复了52处百里香草地,并通过割草、放牧控制草皮的高度,红蚁数量随之上升。1983年,大蓝蝶被从瑞典带到英国。到2008年,已有上万只。大蓝蝶成了第一个成功获得重生的濒危蝴蝶物种。

由本文第1段可知:

A.大蓝蝶在英国对其进行保护前就已经灭绝 

B.大蓝蝶的灭绝是因为人们为制作标本而过量捕捉 

C.大蓝蝶标本受欢迎是因为这种蝴蝶难以捕捉 

D.保护区的建设仅起到了保持大蓝蝶种群数量的效果

题型:选择题

排卵性功血的临床表现中下列哪项不正确()

A.黄体功能不足者月经周期正常,月经频发

B.黄体功能不全者与不孕无关

C.子宫内膜不规则脱落者,经期延长,多达9-10天

D.有排卵功能,但黄体功能异常

E.有排卵功能,黄体功能正常,但是经量偏多

题型:选择题

阅读理解

     The day was Thankful Thursday. It's a weekly tradition that my two little girls and I began years ago.

Thursday has become our day to go out and make a positive contribution. On this particular Thursday, we had no idea exactly what we were going to do. At noon, I drove to a McDonald's with my daughters

because they kept complaining that they hadn't had enough to eat at breakfast. There we saw some

homeless people in the street and we bought lunch for them.

     We were about to complete when we found a small woman standing at the corner, asking for change. We handed her some food, and then started to head home. Suddenly from the mirror of the car, I saw the woman waving at us, so I had to turn around and stopped where the small woman stood. She walked to

our car, and said, "Thank you, lady! No one has ever done anything like this for me before." I replied, "Well, I'm glad that we were the first." Feeling uneasy, and wanting to move the conversation along, I asked,

"So, when do you think you'll eat your lunch?" 

     She just looked at me with her huge, tired brown eyes and said, "Oh honey, I'm not going to eat this

lunch." I was confused, but before I could say anything, she continued. "You see, I have a little girl of my

own at home and she just loves McDonald's, but I can never buy it for her because I just don't have the

money. But you know what... tonight she is going to have McDonald's!"

     I don't know if the kids noticed the tears in my eyes. So many times I had questioned whether our Acts of Kindness were too small to have effect on those poor people. Yet at that moment, I realized the truth of Mother Teresa's words: "We cannot do great things - only small things with great love."

1. The author drove to a McDonald's to ______.                              

A. help the homeless people                                        

B. meet the small woman                                                      

C. buy food for the woman's daughter                                  

D. have lunch with her daughters                                            

2. According to this passage, the small woman was ______.                    

A. too happy to stand at the corner                                  

B. too eager to ask for more food                                            

C. too poor to buy McDonald's                                      

D. too busy to care for her daughter                                        

3. What can we know from the passage?                                        

A. The author finally realized what she did was of use to the poor.          

B. The author would stop doing her acts of kindness to the poor.            

C. The author's daughters found their mother cried at the end of the day.  

D. The author's daughters would make friends with the woman's daughter.    

4. What would be the best title of the passage?                              

A. No Pains No Gains                                          

B. No Pleasure Without Pain                                                  

C. No Small Act of Kindness                                        

D. No Sweet Without Sweat                                                    

题型:选择题

少腹逐瘀汤的药物组成包括()

A.当归、川芎

B.蒲黄、五灵脂

C.延胡索、没药

D.官桂、赤芍

E.小茴香、干姜

题型:选择题

皮带跑偏有几种形式?

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