减小铰刀主偏角对铰孔有何影响？
参考答案：减小铰刀主偏角可减小切削层厚度，使切削平稳，能获得较细的表面粗糙度，并能提高铰刀使用寿命。
用所给词的适当形式填空。
1. This book is not _(I), but it's (she).
2. I'm a (China). I'm from (China).
3. He has four____(sheep) and ten (duck).
4. We are (watch) TV with our teacher.
5. Is there (some) tea in the bottle?
6. Let's (play) football together.
7. I would like_ (have) some oranges.
8. She wants_ (buy) some books.
9. Jim is as _(tall) as Ben.
10. She said she felt much_ (good).
11. Lily had three (cup)of (tea).
12. What about (go) (swim)?
13. Ann's friend comes from (Canadian).
计算题：称取1.721g某种硫酸钙的结晶水合物（CaSO4·nH2O）加热，使之失去全部结晶水，这时硫酸钙的质量是1.361g，试计算1mol结晶水合物中含多少摩尔结晶水。
