碾压混凝土坝施工中，压实质检至少每（）小时一次。
A.1
B.2
C.3
D.4
参考答案：B
Mr. and Mrs. Green work in the hospital, but they have no children. So they belong to _____.
A．extended family
B．nuclear family
C．DINK family
D．celibatarianger
井身结构是由下入井内的导管和油层套管及套管外的水泥环组成。
