题目内容
季节变动,是指某些现象由于受自然因素和社会条件的影响,在一年之内比较有规律的变动。
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凡在短期内,现象有周期性规律的规律变动,都不能称为季节变动。
High-speed steel is also___________________(know) as self-hardening steel.
The more carbon the steel contains and the ________________(quick) cooling is, the __________________(hard) it becomes.
High carbon steel may be ____________________(harden) by heating it to a certain temperature and then quickly cooling in water.
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