: The default member and base class access specifiers are different.

This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifiers, member functions, overloaded operators, and so on. Some of them have even written books about C++. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance. Getting this question wrong does not necessarily disqualify you because you will be in plenty of good company. Getting it right is a definite plus.