Although they (work) ____________ in the same company for five years, they know very little about each other’s background.
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The old professor gave us a number of very (help) _______ suggestions.
He said regrettably that he should have treated the experiment as (careful) ________ as he could.
Do you think it useful (argue) ________ with her anymore about this problem?
【单选题】稀有核苷酸主要是在( )中发现的。
A. mRNA
B. tRNA
C. rRNA
D. 线粒体内DNA
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