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问题 选择题

下列所示图象能正确反映对应的实验或事实的是（　　）

ABCD
图象

实验或事实将等质量的镁和铝分别与足量的盐酸反应20℃时，向一杯不饱和的KNO3溶液中逐步加入KNO3晶体向稀盐酸中滴加过量的烧碱溶液将一定质量的碳在密闭容器中（含空气）加热

A．A

B．B

C．C

D．D

答案

A、等质量的镁和铝与足量盐酸反应时，铝产生的氢气多，镁比铝活泼反应快，即铝产生氢气的特点是“多而慢”，在坐标上表现为铝产生氢气的曲线在上方，曲线的斜率比镁小；故A不能正确反映其对应实验操作；

B、20℃时，向一杯不饱和的KNO3溶液中逐步加入KNO3晶体，溶液的溶质质量分数应该变大，达到饱和时就不会发生变化了，故B不能正确反映其对应实验操作；

C、向稀盐酸中滴加过量的烧碱溶液，溶液的起点是pH＜7，随着反应的进行，酸性逐渐减弱，pH变大，到氢氧化钠过量时，溶液的pH＞7，故C不能正确反映其对应实验操作；

D、根据质量守恒定律，化学反应前后物质的总质量不发生改变，故D能正确反映其对应实验操作．

故选D．

填空题

Questions 19-25


·Read the following article from a magazine and answer questions 19-25.
·For questions 19-25, choose the correct answer A, B, C or D.
·Mark your answer on the Answer Sheet.

The Big Easy on the Brink


A Category 5 hurricane would come barreling out of the Gulf of Mexico, It would cause Lake Pontchartrain, north of New Orleans, to overflow, pouring down millions of gallons of water on the city. Then things would really get ugly. Evacuation routes would be blocked. Buildings would collapse. Chemicals and hazardous waste would dissolve, turning the floodwaters into a lethal soup. In the end, what was left of the city might not be worth saving. "There’s concern it would essentially destroy New Orleans," says Suhayda, a water-resources expert at Louisiana State University.
New Orleans has always had a complicated relationship with the water surrounding it. Everyone told the first settlers this was the wrong place to build a city. It is wedged precariously between the mighty Mississippi and Lake Pontchartrain, and most of it was once swampland. Aggravating the problem is the fact that much of New Orleans is below sea level, so that after a good rain, the water just settles in. There is now a decent pumping system, which helps. Old-timers, however, still talk of the days when, after a bad storm, bodies were washed out of the cemeteries.
What is threatening New Orleans is a combination of two man-made problems: more levees and fewer wetlands. The levees installed along the Mississippi to protect the city from water surges have had an annoying effect: they have actually make it more vulnerable to flooding. That’s because New Orleans has been kept in place by the precarious balance of two opposing forces. Because the city is constructed on 100 feet of soft silt, sand and clay, it naturally "subsides", or sinks, several feet a century. Historically, that subsidence has been counteracted by sedimentation: new silt, sand and clay that are deposited when the river floods. But since the levees went up-mostly after the great flood of 1927—the river has not been flooding and sedimentation has stopped.
New Orleans’ other major man-made problem is that its wetlands and its low-lying barrier islands are disappearing. The Louisiana coast is losingl6,000 acres of wetland each year, mostly as a result of population expansion into once pristine areas, destructive oil and gas drilling, pollution and land loss through lack of sedimentation. As it turns out, wetland, and barrier islands aren’t just nice to look at; they are also a key natural barrier to hurricanes. (Every 2.7miles of wetland absorbs a foot of storm surge.) As the wetlands go, the chance of a hurricane blowing the city away grows.
So far, little has been done to save the city. However, while the grimmest of the doomsayers warn that New Orleans could be next Atlantis, some laid-back residents are saying that it could just as easily become the next Venice and that after the flood, the good times won’t roll—they’ll float.

The rising levees make flooding more likely to happen because ______.

A．they have stopped sedimentation

B．they have blocked the escaping avenues

C．the higher the levees go, the faster the city sinks

D．the levees are not p enough to protect the city
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单项选择题

CT图像伪影的概念，正确的是（）

A.图像中不正常的解剖影像

B.被检体以外物质影像的显示

C.被检体内不存在的影像

D.图像中密度过高或过低的影像

E.影片中图像的变形
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