The correct answer is C. Library header files usually contain function prototypes for functions stored in other files.
A function prototype is a declaration of a function that includes the function’s name, return type, and parameters. It does not include the function’s body. Function prototypes are used to declare functions that are defined in other files. This allows the compiler to check that the function is called correctly, even if the function’s body is not available.
Option A is incorrect because library header files do not usually contain complete functions. Function definitions are typically stored in separate files.
Option B is incorrect because library header files do not usually contain parts of functions. Function prototypes are the only part of a function that is typically stored in a library header file.
Option D is incorrect because library header files do not usually contain function bodies. Function bodies are typically stored in separate files.