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【单选题】
电路能形成自激振荡的主要原因是在电路中( )。A.
引入了负反馈
B.
引入了正反馈
C.
感线圈起作用
D.
供电电压正常
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反馈参考答案：
举一反三
【简答题】国外交易所规定，套利的佣金支出与一个回合单盘交易的佣金相比（ ）。
【多选题】What are the functions of ribozymes?
A.
The best-characterized ribozymes are the self-splicing group I introns, RNase P, and the hammerhead ribozyme. Most of the activities of these ribozymes are based on two fundamental reactions: transesterification and phosphodiester bond hydrolysis (cleavage).
B.
The substrate for a ribozyme is often an RNA molecule, and it may even be part of the ribozyme itself. When its substrate is RNA, the RNA catalyst can make use of base-pairing interactions to align the substrate for the reaction.
C.
Ribozymes vary greatly in size. A self-splicing group I intron may have more than 400 nucleotides. The hammerhead ribozyme consists of two RNA strands with only 41 nucleotides in all. As with protein enzymes, the 3D structure of ribozymes is important for function.
D.
Ribozymes are inactivated by heating above their melting temperature or by addition of denaturing agents or complementary oligonucleotides, which disrupt normal base-pairing patterns. Ribozymes can also be inactivated if essential nucleotides are changed.
【简答题】核酶（ribozymes）
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