Answer:
Operating System.
Explanation:
Operating system (OS) is a software that sits between applications and underlying hardware.
One of OS's main job is to manage hardware resources, and keep a certain balance so that the end-user never experience any major slowdown or freeze while using the system.
For an application to access system hardware, it needs to use the SDK provided by the OS manufacturer. By developing applications through SDK, its developer conforms to what the OS requires for an application to run properly.
