How can cabin crew access a closed aircraft with mobile steps attached to the L2 door?

Accessing a closed aircraft with mobile steps attached to the L2 door involves following specific procedures that allow cabin crew to safely enter the aircraft. In this scenario, option C correctly describes the process.

When mobile steps are in use at the L2 door, cabin crew members must open the L2 door in conjunction with established safety protocols designed to ensure that all steps are properly taken when accessing the aircraft. These procedures typically include verifying that the steps are securely in place and that the area is clear of any hazards before opening the door. This guarantees not only the safety of the crew but also that of any passengers or ground personnel nearby.

The other options suggest methods that are not standard procedures and do not align with safe operational practices; for instance, climbing through an emergency exit or waiting for the flight crew may result in delays or unsafe access. Using a key to unlock the door is not typical for cabin crew and could compromise security protocols. Hence, following the established procedures to open the L2 door is the safest and most effective way for cabin crew to access the aircraft.