戴维宁等效电路是指一个有源二端网络可以用（）和一个（）的串联组合等效，其中电阻值等于原有源二端网络除源后的（），电压源的电压等于原有源二端网络的（）电压。
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Q: How many electives will the woman take for next semester?[音频]
A) 3．
B) 4．
C) 5．
D) 6
2.Q: How long does it take to cycle from the teaching building to the library?[音频]
A) About 5 minutes．
B) About 10 minutes．
C) About 15 minutes．
D) About 20 minutes
3.Q: How many pages does the novel have?[音频]
A) 430．
B) 440．
C) 450．
D) 460．
4. Q: What was Tim’s score in the economics test?[音频]
A) 19．
B) 80．
C) 90．
D) 100．
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