[spoiler]this is the question from gmatclub. and i dont understand why the answer is D instead of C, can you guy take a look and it and explain me why?[/spoiler]

Recently, the research and development departments at major pharmaceutical companies have been experimenting with new injections that provide the boost in iron that anemic children need to reverse their condition. These companies have expressed confidence that children who are suffering from anemia will be cured relatively simply through the use of such biochemical supplements.

In concluding that the biochemical remedy being developed will have its desired effect, the pharmaceutical companies assume that

major pharmaceutical companies have the primary responsibility to cure childhood anemia
a low iron level in the body is the major factor influencing the incidence of anemia in children
a diet rich in iron cannot improve the conditions of children suffering from anemia to the point that biochemical supplements would become unnecessary
children afflicted with anemia will find out about and submit to injections that can reverse their conditions
the use of biochemical supplements is the safest way to cure anemia in children