职工代表实行（），两年或几年改选一次。
A.连任制
B.常任制
C.委任制
D.上级指派
参考答案：A
All the tasks___________ahead of time, they decided to go on holiday for a week. [ ]
A. been fulfilled
B. were fulfilled
C. having been fulfilled
D. had been fulfilled
电刷镀中，一般单一金属镀层不能超过（）mm的安全厚度。
A、0.01～0.02
B、0.02～0.03
C、0.03～0.05
D、0.05～0.06
