Four positive edge-triggered D flip-flops are used to store a 4-bit binary number as shown below. Determine if the circuit is functioning properly, and if not, what might be wrong.

• A. The circuit is functioning properly.
• B. Q2 is incorrect; the flip-flop is probably bad.
• C. The input to flip-flop 3 (D2) is probably wrong; check the source of D2.
• D. A bad connection probably exists between FF-3 and FF-4, causing FF-3 not to reset.