尺寸标准公差分为（）等级。
A、8个
B、10个
C、16个
D、20个
参考答案：D
计算题
1. What percentage of area is shaded?
Answer: _ .
2. If a group of 6 people have an average age of 21, and each person is half the age of the next person,
what are the ages of the 6 people?
矿石经过选刷后，有大量残余的脉脉石，这种残余的脉石称（）
