垫片按照材料和结构可以分为（）。
A、金属包垫
B、非金属垫片
C、金属复合垫片
D、金属垫片
参考答案：B, C, D
计算：978÷5≈
If we can ___ our present difficulties, then everything should be all right. [ ]
A. come across
B. get over
C. come over
D. get off'
