Since 1998, Interest Rate Variability in the Fed Funds Market

Since 1998, interest rate variability in the fed funds market has decreased because

A) fewer institutions were allowed to participate in the fed funds market.
B) of the introduction of lagged reserve accounting.
C) new securities were approved that participants can use instead of fed funds to meet liquidity needs.
D) of the introduction of contemporaneous reserve accounting.
E) more participants were allowed to enter the fed funds market.