Write the next sentence in the following story.

How to understand the basic operation of the home air conditioning system
Understand what the compressor does.
The compressor is the heart of a basic home air and heat unit. It pumps vapor refrigerant through the system and maintains the internal pressure of your home unit based on the temperature of it surroundings.

Choices:
1). The compressor requires a regular indoor refrigerator for it to operate. The compressor shouldn't be heated more than 1800-2500 degrees fahrenheit.
2). It inflates and insulates the warm, humid air inside the unit. In order to function properly in your home, you must develop a universal thermostat that controls the temperature and heats your home continuously.
3). Most homes do not have any type of manual compressor. Basic compressors do not have any type of control or direction.
4). Understand the role of the condenser. This is where the refrigerant goes once it leaves the compressor.. The answer should be
4).