Answer:
c
Step-by-step explanation:
Easiest way is drawing the vectors.
If you need a better reason you can get it through dot product.
Let X be the angle needed.
Dot product of two vectors is defined as
A •B = |A||B|cosX
where X is the angle between A and B
cosX=A•B/ |A||B|
=(-1×-9+1×0) / (√(-1^2+1^2)×√(-9^2))
=1/√2
So the answer is X=45°