混凝土垂直泵送管道不得直接装接在混凝土泵的输出口上,应在垂直管前端加装长度不小于()m的水平管,并在水平管近泵处加装逆止阀。
A.25
B.20
C.15
D.10
参考答案:B
在沙土上栽种______能够防风固沙.
---It's very kind of you to see me off,Mr Johnson.
---______.It's the least we could do.
A.That's true
B.Not at all
C.I don't think so
D.Don't say to