Here is the start of a class declaration:

class foo

$\{$

public:

void $x($foo $f)$;

void $y($const foo $f)$;

void $z($foo $f)$ const;

Which of the three member functions can alter the PRIVATE member variables of the foo object that activ the function?

Only $z$ can alter the private member variables of the object that activates the function.

Two of the functions can alter the private member variables of the object that activates the function.

Only y can alter the private member variables of the object that activates the function.

Only $x$ can alter the private member variables of the object that activates the function.

All of the functions can alter the private member variables of the object that activates the function.