Under MSRB rules, any claim, dispute, or controversy shall be submitted to arbitration at the instance of a:______.
1. broker-dealer against another broker-dealer.
2. customer against a broker-dealer.
3. broker-dealer against a customer who has previously signed an arbitration agreement.
4. broker-dealer against a customer who has not previously signed an arbitration agreement.
a. 2 only.
b. 3 and 4.
c. 1, 2, 3.
d. 1, 2, 3, 4.