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Christiaan Eijkman shared the Nobel Prize in 1929 for the discovery of vitamins. Eijkman went to Java to isolate the pathogen causing beriberi, an illness that appeared to be contagious as it was common in prisons and among ship crews. Eijkman noticed that chickens fed a diet of white rice also suffered from a similar disorder. When the chickens were fed a diet of red rice, the chickens quickly recovered. What can Eijkman safely infer at this point from his observations?

A. Humans with symptoms similar to those of chickens should change their diet.
B.White rice contains little nutritional value for humans and chickens.
C. Beriberi is most certainly not a pathogen.
D. Diet may be the cause of beriberi, but more research is needed.