The European Central Bank's Equivalent of the Fed's Open Market

The European Central Bank's equivalent of the Fed's open market operations (OMO) is:

A) very similar to the Fed's OMO in that they are highly centralized.
B) dissimilar to the Fed's OMO in that the operations are conducted at all 18 of the National Central Banks simultaneously.
C) similar to the Fed's OMO in that they accept only U.S.Treasury securities in their refinancing operations.
D) dissimilar to the Fed's OMO because fewer banks participate in the auctions of the securities.