Suppose That Britain Pegs the Pound to Gold at the Market

Suppose that Britain pegs the pound to gold at the market price of £6 per ounce, and the United States pegs the dollar to gold at the market price of $36 per ounce. If the official exchange rate between pounds and U.S. dollars is $5 = £1. Which of the following trades is profitable?

A) Start with £100 and trade for $500 at the official exchange rate. Redeem the $500 for 13.89 ounces of gold. Trade the gold for £83.33.
B) Start with $100 and buy gold. Sell the gold for £16.67. Sell the pounds at the official exchange rate.
C) Start with £100 and buy gold. Sell the gold for $600.
D) Start with $500 and trade for £100 at the official exchange rate. Redeem the £100 for 16 2/3 ounces of gold. Trade the gold for $600.