What should any C++ base class that maintains pointers to dynamically allocated memory define?
The issue of this question is so important that a class that implements the correct answer is called the canonical class in some literature.  Canonical denotes religious truth.

A copy constructor, assignment operator, and a virtual destructor
This is the correct answer.  It is essential to remember these requirements.  (Stroustrup 10.4.1, 10.4.4.1, 12.4.2.)