Answer:
Explanation: D
Displacement is a vector. It has direction and it has magnitude. But we are asked for the resultant displacement. You have to use pythagorean theorem. This makes our answer always positive. That essentially means distance, since you did just do the distance formula.
A is wrong because that tells you perimeter
B is wrong because that tells you the midpoint
C is wrong because displacement and distance are two different things. We dont want the distance of the two vectors
D is correct, this perfectly explains the distance formula