$A$ voltmeter with internal resistance of $x\text{ }\Omega$ can be used to measure up to $20\text{ V}$. In order to increase its measuring range to $30\text{ V}$,the required modification is to . . . . . . .

• A
  connect a resistor of $\frac{x}{2}\text{ }\Omega$ in series with the voltmeter.
• B
  connect a resistor of $\frac{x}{2}\text{ }\Omega$ in parallel to the voltmeter.
• C
  connect a resistor of $x\text{ }\Omega$ in series with the voltmeter.
• D
  connect a resistor of $2x\text{ }\Omega$ in parallel to the voltmeter.