What does the presence of a vestigial structure in a modern organism indicate?

Question

a
Natural selection perpares the body of organisms so that in the future the vestigial structures may be used
b
A limited number of genes are expressed during the lifetime of an organism
c
The vestigial structure was not used by the modern organism, so it became nonfunctional within the organism's lifetime
d
The structure was probably functional in some ancestor of the modern organism

Answer 1

d. The structure was probably functional in some ancestor of the modern organism