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【多选题】
采用溴化钾压片法制备试片时,一般要求A.
样品与溴化钾要在研钵中研磨混匀
B.
溴化钾一定是经过干燥处理的
C.
一般要在红外灯下，将样品与溴化钾在玛瑙研钵中研匀
D.
压片操作要在红外灯下进行
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知识点：
皮皮学刷刷变学霸
举一反三
【单选题】At the time of the earthquake Jeff was still in his office. He ________ to finish a project before he left for the day.
A.
has tried
B.
had tried
C.
has been trying
D.
had been trying
【简答题】He must finish his homework by today. must调到句首
【简答题】If he (finish)______his work on time, he will go for a picnic with his friends tomorrow.
【简答题】引入批处理系统的目的是为了提高 ____________ 。
【简答题】在分时和批处理系统结合的操作系统中引入了“前台”和“后台”作业的概念,其目的是 。