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(1) According to the circuit diagram, the power supply consists of dry cells with a voltage of1.5v.,

According to ohm's law, the size of the resistance is:

r = UI = 1.5v 0.2a = 7.5ω；

(2) When the primary battery is connected in series with another identical battery, the power supply voltage is 3V.

∫ Resistance is the nature of the conductor itself, which has nothing to do with the voltage at both ends and the current passing through it.

∴ current through resistor at this time:

I′= U′R = 3v 7.5ω= 0.4a。

So choose B.