Which of the following statements is true (in C++)?

1)

For a function to be virtual in a derived class, it must be virtual in the base class.

2)

For a function to be virtual, its object parameter(s) must be passed by reference to the derived function.

3)

If a virtual function has its parameters passed by reference, the actual parameter, not the formal parameter, determines which function to use.

4)

All of these statements are true.

5)

None of these statements is true.