单项选择题

甾体激素类药物能与羰基试剂发生呈色反应,是因其结构中有( ) A.
C3-酮和C20-酮 B.
卤素 C.
乙炔基 D.
酚羟基

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多项选择题

定向方式是为了将广告受众人群限定在一定范围内，实现更精准的触达，提高投资回报率。定向要（） A、避免过窄 B、避免交叉 C、避免竞争 D、避免重叠

判断题

When you begin to introduce the purpose of your paper and the specific problem you will deal with, it is necessary to create a research space. You can do this either by describing a problem in the previous research or by indicating that there is a gap in the research.

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