On the ERJ 175, the role of the FWD FA regarding the MCD is to:

The correct choice reflects the Forward Flight Attendant's responsibilities concerning the Main Cabin Door (MCD) on the ERJ 175. The FWD FA is tasked with both opening and closing the MCD throughout various phases of flight, particularly during boarding, deplaning, and when preparing for departure. This dual responsibility ensures that the door is securely shut when the aircraft is in operation and properly opened when it is safe for passengers to embark or disembark.

By being involved in both actions, the FWD FA ensures compliance with safety protocols and passenger convenience. The role is critical because operating the MCD correctly minimizes potential safety risks associated with cabin pressure, emergency evacuations, and general accessibility for passengers.

While observing its operation is important, the FWD FA must actively engage with the door as part of their duties. Therefore, simply closing or just observing its operation would not encompass the full scope of responsibility that the FWD FA has concerning the MCD. Similarly, maintenance of the door falls under different job functions that are not the direct responsibility of the FWD FA. Overall, the chosen answer accurately captures the active role of the FWD FA in managing the MCD on the ERJ 175.