题目内容
（请给出正确答案）
[主观题]
对制备测定某些金属含量的干样品时，为避免受金属器械和筛子等污染，最好用______磨碎，______过筛，______保存
。
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Some people really like to get up early in the morning. They enjoy being awake (醒来) before the mst of the world. They also get a lot of work done early in the day. We call these kinds of people morning people. Other people like to sleep late. They enjoy being awake at night when the mst of the world is sleeping. They get a lot of work done late at night. These people are called night owts (猫头鹰).
There am ______ kinds of people in this passage (短文).
A．two
B．three
C．four
