— ________ pens do you have?
— I have 11 pens.[ ]
A. How much
B. How many
C. How
答案:B
_________ jump on the train![ ]
A. Not
B. don't
C. Don't
下列不能提高对流传热膜系数的是()。
A、利用多管程结构
B、增大管径
C、在壳程内装折流挡板
D、冷凝时在管壁上开一些纵槽