The dot product of.two vectors is -1which of the following statements is true
A. They must be unit vectors pointing in opposite directions.
B. They must be unit vectors pointing j. The same direction.
C. They must be more than 90( and less than 270 )degrees from each other.
D. They must be perpendicular to each other.
E. They must sum to zero
I have eliminated D though I find the others difficult