Resolve the paradox

Raisins are made by drying grapes in the sun.
Although some of the sugar in the grapes is
caramelized in the process, nothing is added.
Moreover, the only thing removed from the grapes is
the water that evaporates during the drying, and
water contains no calories or nutrients. The fact that
raisins contain more iron per calorie than grapes do is
thus puzzling.
Which one of the following, if true, most helps to
explain why raisins contain more iron per calorie
than do grapes?
(A) Since grapes are bigger than raisins, it takes
several bunches of grapes to provide the
same amount of iron as a handful of raisins
does.
(B) Caramelized sugar cannot be digested, so its
calories do not count toward the calorie
content of raisins.
(C) The body can absorb iron and other nutrients
more quickly from grapes than from raisins
because of the relatively high water content
of grapes.
(D) Raisins, but not grapes, are available yearround,
so many people get a greater share of
their yearly iron intake from raisins than from
grapes.
(E) Raisins are often eaten in combination with
other iron-containing foods, while grapes are
usually eaten by themselves.