If the Fed Desires to Weaken the Dollar Without Affecting

If the Fed desires to weaken the dollar without affecting the dollar money supply, it should:

A) exchange dollars for foreign currencies, and sell some of its existing Treasury security holdings for dollars.
B) exchange foreign currencies for dollars, and sell some of its existing Treasury security holdings for dollars.
C) exchange dollars for foreign currencies, and buy existing Treasury securities with dollars.
D) exchange foreign currencies for dollars, and buy existing Treasury securities with dollars.