Read the question and help me with that, please.

Answer:
B. -1
Step-by-step explanation:
examples:
1 and -1
1/2 and -2
Answer:
B=-1
Step-by-step explanation:
diagonals are perpendicular line, the slope of perpendicular line are opposite reciprocal.
example if the slope line AC =3
the slope of BD=-1/3
-1/3*3=-1