A study of expectant mothers suggests that thin women can significantly increase their chances of bearing bigger babies by taking zinc supplements during pregnancy. Three hundred women who took 25 milligram zinc supplements starting with the 19th week of pregnancy were compared to 250 women who took placebos. All the women also took a multivitamin-mineral supplement containing no zinc. Babies born to the zinc group weighed five ounces more on average with the greatest gain among thin women; for example, women in the zinc group who were 5'4'' tall and weighed under 110 pounds had babies one pound heavier, on average, than those born to similar-sized women in the placebo group.

The conclusion drawn in the passage above depends on which of the following assumptions?

A.Zinc found in natural sources, such as sea food, nuts and milk, is not as effective as supplements in increasing a pregnant woman's chances of bearing larger babies.

B.The first 18 weeks of pregnancy did not play a significant role in the result of the study.

C.Zinc supplements have little or no effect on the size of babies born to taller, heavier mothers.

D.Thin women who take more than 25 milligrams of zinc daily will give birth to even larger infants.

E.Zinc supplements have a greater effect on the size of babies born to thin women because women have less zinc stored in their bodies.