Correct Option: C

boundary (Noun) : a real or imagined line that marks the limits or edges of something and separates it from other things or places
frontier (Noun) : a line that separates two countries, etc.
edge (Noun) : the outside limit of an object, a surface or an area something, such as a large building that you can see clearly
landmark (Noun) : something, such as a large building, that you can see clearly from a distance and that will help you to know where you are
corner (Noun) : a part of something where two or more sides, lines or edges join