ANS:C - +28 V

When you have three resistors connected in series with a battery of 28V, and then one resistor is open-circuited (removed from the circuit), the voltage across the remaining resistors will be the same as the battery voltage.

This is because, in a series circuit, the same current flows through all components, and the voltage is divided among the resistors. When one resistor is removed (open-circuited), there is no longer any voltage drop across it, but the battery voltage is still applied to the remaining components.

So, in this case, the voltage across any of the two remaining resistors (which are still connected in series with the battery) will be the same as the battery voltage, which is 28V.