用（）法画组合体的正等轴测剖视图，可先画出其完整的正等轴测图。
A、换面
B、旋转
C、中心投影
D、先画外形再作剖视
参考答案：D
动词填空。
1. I ______(babysit) my sister this evening.
2. Tom ______(visit) his cousins tomorrow afternoon.
3. You want to go to Canada for vacation. When ______you _____(go)?
4. Why not go _______(boat) on the river with me ?
5. We often _______(help) Granny Li ______(do) the housework.
6. China is a good place _______(go) sightseeing.
7. We plan _______(visit) Tibet next year.
8. How about _______(stay) at home this evening?
9. After I finished _______(go) shopping, I cooked at home.
10. He _______(take) a vacation in Hainan last winter.
炉衬的破损原因主要有高温热流的作用、（）、机械冲撞的作用、化学侵蚀等几方面作用。
