An Uncharged,series RC Circuit Is Connected Across a Battery

Multiple Choice

An uncharged,series RC circuit is connected across a battery.For which situation will the time for the capacitor to reach 90% of its final charge remain unchanged?​

A) ​The RC time constant is doubled.
B) ​The battery voltage is doubled.
C) ​A second resistor is added in series with the original resistor.
D) ​All of these situations result in the time for the capacitor to reach 90% of its final charge to change.