坝胎回填要分层夯实，干密度达到（）以上。
A.1.5t/m3
B.1.45t/m3
C.1.4t/m3
D.1.55t/m3
参考答案：A
—______ I use your mobile phone?
—Certainly. Here you are. [ ]
A. May
B. Must
C. Should
D. Need
旅行社业务经营许可证有效期为（）年。
A.1
B.2
C.3
D.5
