一般情况下，多层建筑物墙体选用()的砌筑砂浆;砖石基础、检查井、雨水井等砌体，常采用()砂浆;工业厂房、变电所、地下室等砌体选用()的砌筑砂浆;二层以下建筑常用()砂浆;简易平房、临时建筑可选用石灰砂浆;一般高速公路修建排水沟使用()强度等级的砌筑砂浆。

A. Because they are a part of the environment.
Because of twenty-five years of progressive environmental legislation.
C. Because they set the standard for land stewardship in America.
D. Because millions of people visit them each year.

A. raise awareness of the needs of national parks
B. allow roads to go through national parks
C. eliminate national parks
D. help save national parks

A. to describe recent environmental policy
B. to point out the difficulties inherent in protecting national parks
C. to call for the protection of national parks
D. to analyze the current status of national parks