Final answer:
Flight attendants use a special method to unlock airplane lavatory doors in case of an emergency, involving a hidden latch or button. This safety feature ensures access when necessary. Thus, the correct option is (A) He uses a key.
Step-by-step explanation:
Flight attendants are trained professionals who ensure the safety and comfort of passengers aboard an aircraft. In case of an emergency or if necessary, there is indeed a protocol for flight attendants to access a locked lavatory. Airplane lavatories have a built-in mechanism that allows access from the outside in special situations. Contrary to what might be seen in movies, breaking the door down or calling a locksmith are not options. Also, it's important to note that airplane lavatories do not have windows that would allow for entry or exit, making that option implausible.
The actual method to open a lavatory door from the outside usually involves a hidden latch or button that releases the lock. This is generally located in a discreet area, often under the "lavatory" sign or behind a panel that can be carefully opened by the flight attendant. This is a safety feature designed to ensure that a flight attendant can access the lavatory if someone is in distress or if there's another urgent situation where entry is necessary. Therefore, the correct answer is (A) He uses a key, with the understanding that 'key' in this context often refers to a specific tool or method rather than a traditional metal key.
To summarize, while there is no traditional key like one might use for a house or a car, there is a special method for unlocking the lavatory door that is part of the safety protocols known by flight attendants.