What is a ruler?

A. It is a straight line used to highlight a banner or carve a document into sections
B. It is the margin present to the right of the text.
C. It is a guideline that should be followed for the design of all documents
D. It is a reference to an entry in an appendix

1)consider the following code snippet: #ifndef book_h#define book_hconst double max_cost = 1000.0; class book{public: book(); book(double new_cost); void set_cost(double new_cost); double get_cost() const; private: double cost; }; double calculate_terms(book bk); #endifwhich of the following is correct? a)the header file is correct as given.b)the definition of max_cost should be removed since header files should not contain constants.c)the definition of book should be removed since header files should not contain class definitions.d)the body of the calculate_terms function should be added to the header file.