Question

read the passage. when someone walks up to a stores sliding glass door, it opens like magic. but what makes the door open? automatic doors operate with a device called a sensor to open the door when someone is nearby. many sensors send out infrared light, a type of light that humans cant see. this light reflects off the floor and back to the sensor in a steady pattern. when a person approaches the door, they walk through that light. since the body blocks light, the sensor recognizes an interruption in the pattern. so when this happens, the sensor sends a signal to a motor in the door frame, which makes the door open. how does the author structure this text? by contrasting sensors that send out light to sensors that send out radio waves by introducing the problem humans face when approaching a sliding glass door by describing how sliding doors have impacted sensors within buildings by explaining how a sliding door uses a change in a light pattern to operate

Explanation:

The passage starts with the phenomenon of automatic - sliding glass doors opening, then explains how sensors using infrared light detect a person's presence by a change in the light pattern and send a signal to open the door. It focuses on the operation principle of the sliding door based on light - pattern changes.

Answer:

by explaining how a sliding door uses a change in a light pattern to operate