单选题：Which of the following statements are true?
Which of the following statements are true? @[A](2)
A. A custom exception class is just like a regular class.
B. A custom exception class must always be derived from class exception.
C. A custom exception class must always be derived from a derived class of class exception.
D. A custom exception class must always be derived from class runtime_error.
A.A custom exception class is just like a regular class.
B.A custom exception class must always be derived from class exception.
C.A custom exception class must always be derived from a derived class of class exception.
D.A custom exception class must always be derived from class runtime_error.
答案：A
A. A custom exception class is just like a regular class.
B. A custom exception class must always be derived from class exception.
C. A custom exception class must always be derived from a derived class of class exception.
D. A custom exception class must always be derived from class runtime_error.
A.A custom exception class is just like a regular class.
B.A custom exception class must always be derived from class exception.
C.A custom exception class must always be derived from a derived class of class exception.
D.A custom exception class must always be derived from class runtime_error.
答案：A