问题 单项选择题

硅酸盐水泥的终凝时间不得长于()。

A.6.5h

B.7.5h

C.8.5h

D.10h

答案

参考答案:A

解析:此题比较专业,有一定的难度,主要考核最常用建筑材料中水泥凝结时间的知识点。水泥的凝结时间分初凝时间和终凝时间。初凝时间是从水泥加水拌合起至水泥浆开始失去可塑性所需的时间;终凝时间是从水泥加水拌合起至水泥浆完全失去可塑性并开始产生强度所需的时间。国家标准规定,六大常用水泥的初凝时间均不得短于45min,硅酸盐水泥的终凝时间不得长于6.5h,其他五类常用水泥的终凝时间不得长于10h。故本题的正确项为"A.6.5h"。

阅读理解

In “Relax, We’ll Be Fine”, columnist David Brooks writes, “the fact is, despite all the problems, America’s future is extremly bright.”

Mr. Brooks acknowledges that “According to recent survey, 60 percent of Americans think the country is heading in the wrong direction. The same percentage believe that the U.S. is in long-term decline. The political system is not functional. A financial crisis looks unavoidable. There are plenty of reasons to be sad.”

But, he writes:

“Demographers(人口学家) predict that over the next 40 years, the U.S. population will increase by an additional 100 million people, to 400 million over all. The population will be determined, hardworking and relatively young. In 2050, only a quarter will be over 60, compared with 31 percent in China and 41 percent in Japan.”

As the rising generation leads an economic recovery, it will also participate in a communal

(of community) one. We are living in a global age of social entrepreneurship(创业精神).

In sum, the U.S. is on the edge of a demographic, economic and social recovery, built on its historic strengths. The U.S. has always been good at destructive change. And it’s always been good at decentralized community-building, too. Surely a country with this much going for it is not going to wait around passively and let a rotten political culture drag it down.

51.In his article Relax, We’ll Be Fine, David Brooks intends to____________.

A.encourage Americans to be optimistic about their future

B.give Americans courage to face their financial crisis

C.persuade Americans to live happily and generously

D.inspire Americans to lead an economic recovery

52.There are all the reasons for Americans to be unhappy except____________

A.the function-failed political system         B.the increasing population

C.the declining economy                   D.the wrong direction and financial crisis

53.Over the next 40 years, according to David Brooks, Americans will be____________

A.more optimistic and humorous            B.more pessimistic and stronger

C.more energetic and promising             D.more considerate and aggressive

54.In the author’s opinion, America____________.

A.has always benefited from wars            B.has done well by its political system

C.has contributed a lot to human progress     D.has contributed to world’s economy

55.We can learn from the passage that____________

A.American political system and culture are backward

B.Americans are not a nation to give in to difficulties

C.Americans are very destructive and aggressive

D.America has been in an economic and social recovery

单项选择题