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【单选题】
用感应加热器加热轴承内圈或防尘板（挡圈）时，在工件套入之前（）。
A.
不得通电加热
B.
应通电预热
C.
应断续通电预热
D.
通电或不通电均可
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参考解析：
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【单选题】Most shoppers know the feeling. You stand in front of piles of organic produce and wonder what those premium prices are buying you over and above what you get from standard foods. Not a lot nutrition-...
A.
do not use naturally produced fertilisers
B.
produce carbon dioxide when removing weeds
C.
use high doses of weed-killer
D.
use too many resources to qualify for organic status