[单选题]
Action-reaction forcu4hbq.i upqyoj; z8 :vvq(t-*esgk 0*qzum)xl7 k :o h*fqz9us0t9zg z) are
A. equal in magnitude and point in the same direction.
B. equal in magnitude but point in opposite directions.
C. unequal in magnitude but point in the same direction.
D. unequal in magnitude and point in opposite directions