We have a figure that could be a square or a rhombus, and we have to choose the correct statement.
So,let's analize each statement:
A. KM and JL are perpendicular - This is true for square and rhombus
B. KM and JL are parallel - the diagonals could not be parallel.
C. JM and LM are parallel - The adjacent sides could not be parallel.
D. JL and LM are perpendicular - JL bisects the angle MLK, so if JL and LM are perpendicular the angle MLK must be 180° and this is not possible for adjacent sides, so this statement is false
The correct statement is A, the diagonals of a square or a rhombus are perpendicular.