Final answer:
Flight attendants receive visual and audible signals when smoke is detected in an airplane lavatory, through alerts on control panels and alarms in crew areas.
Step-by-step explanation:
If smoke is detected in an airplane lavatory, flight attendants typically receive both visual and audible signals. A standard signal system includes a visual alert on the cabin crew's control panel and sometimes onboard monitors, indicating exactly which lavatory has triggered the alarm. Additionally, there is often an audible alarm that may sound in the galley or flight attendant's work areas, enabling them to respond quickly. These signals are designed to be immediate and unmistakable to prompt a rapid response from the crew. Unlike options C or D, vibrations in wristbands or scented notifications are not standard methods of alert in commercial aircraft.