He found          difficult to improve his English          the teacher’s help.

A．it is; without

B．it was; with

C．it; without

D．that is; with

非节奏流水施工的特点有（）。

A．各施工过程在各施工段的流水节拍均不相等

B．相邻施工过程的流水步距不尽相等

C．专业工作队数等于施工过程数

D．有的施工段可能有空闲时间

E．各专业工作队能够在施工段上连续作业