空速大小对甲醇合成的影响有哪些？

水泥石灰砂浆罩面拉毛有水泥石灰砂浆和水泥石灰加纸筋砂浆拉毛两种。前者多用于内墙饰面，后者多用于外墙饰面。( )

项目的投资目标、进度目标和质量目标之间是（）。

A.相互对立的关系

B.相互统一的关系

C.相辅相成的关系

D.对立的统一关系

不适用于压力容器、压力管道的材料是()。

A.碳素结构钢 

B.优质碳素结构钢 

C.低合金结构钢 

D.不锈钢 

E.玻璃钢

根据检疫机构签发的产地证书是进口国海关征收或减免关税的有效凭证。( )

Believe it or not，optical illusion can cut highway crashes.
Japan is a case in point．It has reduced automobile crashes on some roads by Rearly 75 percent using a simple optical illusion．Butst．ripes,called chevrons(人字形)，painted on ther rads make drivers think that they are driving faster than they really are，and thus drivers slow down.
Now the American Automobile Association Foundation for Traffic Safety in Washington D．C. is planning t。repeat Japan’s success．Starting next year，the foundati。n will paint cheyrons and。ther pattems of stripes on selected roads around the country to test how well the patterns reduce highway erashes．
Excessive(too great)speed plays a major role in as much as one fifth of all fatal traffic accidents， according to the foundation．To help reduce those accidents，the foundation will conduct its tests in areas where speed-related hazards(danger)are the greatest curves，exit slopes，traffic circles，and bridges．
Some studies suggest that straight，horizontal bars painted across roads can initially cut the average speed of drivers in half．However,traffic。ften returns to full speed within months as driVers become used to seeing the painted bars．
Chevrons，scientists say，not only give drivers the impression that they are driving faster than they reallv are but als0 make a lane appear to be narrower．The result is a longer lasting reduction in highway speed and the number of traffic accidents．

What does the author say about straight,horizontal bars painted across roads

A. They are suitable only on broad roads.
B. They are falling out of use in the United States.
C. They are ignored in a long period of time.
D. They cannot be used successfully to traffic circles.