Study the header file code in the following code snippet:

#ifndef CAR$\_$H

#define CAR$\_$H

class Car

$\{$

public:

Car$()$;

Car$($double speed$)$;

void start$()$;

void accelerate$($double speed$)$;

void stop$()$;

double get$\_$speed$()$ const;

private:

double speed$1$;

$\}$;

Car::Car$()$

$\{$

speed$1=0$;

$\}$

#endif

Which of the following is true about placing the function definition Car::Car$()$ in the header file?

Question $4$ options:

Function definitions cannot be enclosed within header files. It will result in a compilation error.

Function definitions should not be enclosed within header files. The header file may be included by multiple source files, which would cause the function to be compiled more than once.

Function definitions must always be enclosed within the header files but not the source files.

Function definitions must always be enclosed within the header files and the source files.