At 10 Cents Per Kilowatt- Hour, How Much Does It

At 10 cents per kilowatt- hour, how much does it cost to run a 100 watt lightbulb for 200 hours every month?

A) 20 cents per month
B) $2 per month
C) $20 per month
D) impossible to determine because we don't know the voltage
E) impossible to determine because we don't know the power