燃油锅炉点火时,应保证炉膛负压在()Pa。
A.10至20
B.20至30
C.30至40
D.50至100
参考答案:D
The number of teachers in our college __________greatly increased last term.A number of teachers in this school __________from the countryside.
A.was; is
B.was; are
C.were; are
D.were; is
维持柴油机运转,控制电路中必须保持RBC线圈,DLS线圈通电。