五项管理职能之间，按发生先后顺序应为（） A.计划、组织、领导、决策、控制 B.

He didn’t _____ to what I said because his mind was on something else.

A．hold on

B．take in

C．catch on

D．get over

设x，y是满2x+y=4的正数，则lgx+lgy的最大值是______．

He has made a_________offer-he will make it clear as soon as possible.  [ ]

A. sure          

B. certain      

C. tentative  

D. clear

络合滴定方式有（）滴定法，（）滴定法，（）滴定法（）滴定法四种。

常用的聚合物基体有哪些？三种常用热固性树脂各有何主要特点？各自主要适合于哪种（些）增强纤维？