Answer:
b. the Federal Reserve System.
Step-by-step explanation:
Initial margin refers to the deposit made by an investor with a broker, in order to open a margin account. The purpose of initial margin is security and collateral to ensure enough availability of cash in the trading account of the investor.
For instance an investor wants to purchase 4000 shares priced at 15$. In this case, he is supposed to deposit 50% of $60,000 i.e $30,000. The remaining $30,000 is contributed by the brokerage firm, regarded as borrowings on which the investor pays interest.
The initial margin limit is fixed by the Federal Reserve System.