冷缝
参考答案：上下两层混凝土浇筑的时间间隔如果超过初凝时间，便产生冷缝。冷缝造成两层之间的抗拉、抗剪及防渗性能减弱，混凝土浇筑不允许产生冷缝。
There are many places in the world ________ have been visited only by a few, many ________
are of an enormous beauty.[ ]
A. where; of which
B. which; of whom
C. that; of which
D. that; of whom
耕地作业前应将地块划为若干作业区，测算好使其宽度等于机组工作幅宽的（）。
A.单倍数
B.双倍数
C.整倍数
D.2倍数
