Data Structures using C++

Here is the start of a class declaration:

class ClassA

{

public:

void func1(const ClassA& a);

void func2(const ClassA& a) const;

void func3(ClassA a) const;

...

Which of the three member functions can alter the private member variables of the ClassA object that activates the function?

A. None of the three functions.

B. Only func1

C. Only func2

D. Only func3

E. Only two of the three functions