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【简答题】
下列关于燃料的说法中，正确的是（ ） A．石油是纯净物 B．化石燃料是取之不尽、用之不竭的 C．煤、石油和酒精都是化石燃料 D．煤和石油的燃烧会造成对空气的污染
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举一反三
【简答题】胆固醇生物合成的原料是______。
【单选题】Voltage-series feedback ( ) the output impedance of an op-amp.
A.
increases
B.
decreases
C.
reduces by half
D.
has no effect on
【单选题】The impedance of an RLC series circuit is definitely decreased if:
A.
R decreases
B.
R increases
C.
L increases
D.
C increases
【单选题】Current-series feedback ( ) the input impedance of an op-amp.
A.
increases
B.
decreases
C.
reduces by half
D.
has no effect on
【单选题】Voltage-series negative feedback ( ) the input impedance of an op-amp.
A.
increases
B.
decreases
C.
reduces by half
D.
has no effect on
【单选题】The input impedance of the base of an emitter follower is usually______
A.
high.
B.
shorted to ground.
【单选题】Voltage-series feedback ( ) the input impedance of an op-amp.
A.
increases
B.
decreases
C.
reduces by half
D.
has no effect on
【单选题】Current-series feedback ( ) the output impedance of an op-amp.
A.
increases
B.
decreases
C.
reduces by half
D.
has no effect on
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