The correct option is
C Legend
A map legend or key is a visual explanation of the symbols used on the map. It typically includes a sample of each symbol (point, line, or area), and a short description of what the symbol means.
Various symbols are represented on a map to show the human and physical features and they are classified as Legend.
Like for representing the river , mountains and lakes i.e physical features on a topographic map the cartographers used small size symbols with specific colors to describe the exact figure which is being represented on the map.
Similarly, for the case of human features, the map depicts either a cross for church or a dotted line for pathway or some sort of sign for that object. Use of letter symbols are also done in order to represent the natural vegetation like reserved forest R or protected forest P, etc.
Hence, option C is the correct answer.