We often use graphs to simplify optimization problems, as they are easy implement on a computer.The following concepts can be illustrated with a graph. Determine which variables should be represented by edges and vertices in this graph.A school's course catalogSome classes must occur at least one semester before certain other classes (e.g., Calculus I must be taken before Calculus II), but not all classes have prerequisites.If we want to represent the catalog as a graph, which variables should be represented as edges and vertices?

A) Each edge is a class, while different vertices indicate the semester the class is taken.
B) Each vertex is a class, while a directional edge indicates that one class must come before another.
C) Each vertex is a class, while edges between two vertices indicate that the classes may be taken at the same time.