A voltmeter having a resistance of `1800 Omega` employed to measure the potential difference across a `200 Omega` resistor which is connected to the terminals of a dc power supply having an emf of 50 V and an internal resistance of `20 Omega`. What is the percentage decrease in the potential difference across the `200 Omega` resistor as a result of connecting the voltmeter across it?
A. `1%`
B. `5%`
C. `10%`
D. `25%`
