A student finds a resistor in an old transistor radio. When the resistor is attached to a 1.5 V cell, the flow of current is measured at 0.025 A. When the resistor is attached to four 1.5 V cells, the current is measured at 0.1 A. When the resistor is attached to a 9 V battery, the current is measured at 0.15 A. Is the resistor an ohmic resistor? Explain how you know.