中心排水管的管材应符合国家标准《混凝土和钢筋混凝土排水管》(GB/T11836-1999)三级管的要求。
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Never ________ even when you are sad, because you never know who is falling in love with your smile!
A. knit
B. frown
C. known
D. crown
The next morning some experts were sent to ________ the damage caused by the flood.
A. survey
B. research
C. study
D. investigate
The prime minister succeeded in ________ the challenge to his authority(权威).
A. sustaining
B. lasting
C. surviving
D. postponing
The universities will ________new students in August.
A. enlist
B. enroll
C. participate
D. attend