What the "RETURN" does (part a) AND explain what would happen IF the Air Handler did not have a "RETURN" (part b) ​

Returns ensure efficient return of air so that the HVAC system cools down properly

Explanation:

The return parts of the air handler prevents the HVAC system from heating up and ensures its proper cooling.

If there is no return system,  enough air will not be brought back, the air system will not be able to tackle with the problem of temperature demand.

unlike the threaded fasteners which are used to clamp the machine members, power screws are used to transmit power. common applications of power screws are: screw jacks: to lift weight. lead screw of lathe: for axial movement of tool and its precise positioning.

 They're compact and can easily be used for both FWD and RWD vehicles. Allows for greater displacement than inline cylinder engines, typically meaning more power.