What effect does each of the following have on the U.S. monetary base? a. The Fed purchases

Question:

What effect does each of the following have on the U.S. monetary base?
a. The Fed purchases $10 billion of foreign assets.
b. The Fed sells $10 billion of foreign assets and purchases $10 billion of Treasury securities.
c. The Fed conducts a sterilized foreign exchange intervention.
d. The Fed sells $10 billion of foreign assets and sells $10 billion of Treasury securities.