题目内容

病毒感染的血清学反应,要求取双份血清,是因为()

A. 为了提高准确度
B. 观察两次的结果是否一致
C. 观察恢复期抗体效价是否随着病情好转而下降
D. 观察恢复期抗体效价是否比初发期增高
E. 为了提高精密度

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按光波在时间、空间上的相位特征,将光源分为()。

In which two cases would you use an outer join? ()

A. The tables being joined have NOT NULL columns.
B. The tables being joined have only matched data.
C. The columns being joined have NULL values.
D. The tables being joined have only unmatched data.
E. The tables being joined have both matched and unmatched data.
F. Only when the tables have a primary key/foreign key relationship.

利用干酪根的颜色可以评价有机质的()。

A. 组分
B. 成熟期
C. 成熟度
D. 轻烃含量

属于一级信息源的文献是(),优点是()

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