CO2气体保护焊用的CO2气瓶采用电热预热器时，电压应低于()。
A. 60V
B. 36V
C. 12V
D. 6V
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If the water temperature had increased after submerging resistor B, which of the following statements would have been most accurate？
A. The fact that the water temperature increased after submerging Resistor B shows that resistor B is a thermistor.
B. The fact that the water temperature increased after submerging Resistor B shows that resistor B is not an ohmic device.
C. Since the measured current was the same when the initial water temperature was 23°C as when it was 25°C,resistor B is an ohmic device.
D. Since the measured current was the same when the initial water temperature was 23°C as when it was 25°C,resistor B is not a thermistor.
Supporters of all three theories would agree that:
A. imprinted genes evolved as a means of regulating reproduction-related events.
B. imprinted genes should be absent in non-placental animals (animals whose offspring develop without a placenta).
C. if an embryo is formed without female-imprinted genes, the future ability of the mother to bear off-spring will be jeopardized.
D. imprinted genes should always be turned off in the mother.
Supporters of the protein control theory believe that:
A. imprinted genes are used to regulate crucial proteins.
B. imprinted genes are active only in females.
C. imprinted genes should not be found in monogamous species (ones that mate for life).
D. only the male passes down imprinted genes to the offspring.
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