Theorem: A line parallel to one side of a triangle divides the other two proportionately. In the figure below, segment DE is parallel to segment BC and segment EF is parallel to AB. The figure shows triangle ABC with segments DE and DF. Point D is on side AB, point E is on side AC and point F is on side BC. Which statement can be proved true using the given theorem?

a
Segment BF = 9

b
Segment BD = 18

c
Segment BD = 20

d
Segment BF = 24