Question

what was one of the key features of marie van brittan browns home security system? a video camera on a sliding mechanism that allowed users to monitor and record their front door an alert signal that would summon the police or members of the neighborhood watch a motion - activated floodlight and alarm system that would deter anyone attempting to break in

Explanation:

Marie Van Brittan Brown's home security system had a key feature of a video camera on a sliding mechanism to monitor and record the front door. This aligns with the first option, as her invention included a sliding camera setup for surveillance of the entrance. The other options either don't match her specific design (like summoning police/neighborhood watch wasn't the core sliding camera feature, and motion - activated floodlight/alarm was not the defining sliding camera part of her system).

Answer:

a. a video camera on a sliding mechanism that allowed users to monitor and record their front door