If the United States and Britain Were Both on the Gold

If the United States and Britain were both on the gold standard with the dollar worth 1/20 of an ounce of gold and the pound worth 1/5 of an ounce of gold,the exchange rate in terms of the dollar to the pound would be

A) $0.10.
B) $0.50.
C) $1.
D) $4.
E) $5.