政府对运输业进行管制和干预具有明显的（）。
参考答案：阶段性
杠杆平衡的必要与充分条件是：作用在杠杆上各力对于支点力矩的代数和必须（）
A.大于零
B.等于零
C.小于零
D.等于一
The Canadian friends from our school have given us a lot of books, few of ________ a bit difficult for us Chinese students.
A. them are
B. that is
C. which are
D. which is
