某校九年级的一次数学测验中,成绩在80~84分之间的同学有84人,在频率分布表中的频率为0.35,则全校九年级共有学生______人.
由题意得,84÷0.35=240(人).
Mr. Irving, who ____ in a high school for forty years, is now living in retirement. [ ]
A. has taught
B. taught
C. had taught
D. has been teaching
对于管道抹带,直径小于等于()的管道,采用在浇注混凝土管座的同时,在管内来回拖动麻袋球的方法,将流入管内的灰浆拉平。
A.500mm
B.600mm
C.700mm
D.800mm