(单选题)The figure below illustrates the market for British pounds. D£ and S£ are the nonofficial demand and supply curves of the British pounds, respectively.If the British government wants to peg the dollar per pound exchange rate at $2.50 per pound, what action would British monetary authorities have to undertake?
选项：

A: Buy 1 million pounds and sell 1 million dollars
B: Buy 1 million pounds and sell 2.5 million dollars
C:Buy 6 million pounds and sell 12 million dollars
D:Sell 1 million pounds and buy 2.5 million dollar