which of the following most logically completes the passage?

A certain tropical island received food donations in the  form of powdered milk for distribution to its poorest residents, who were thought to be malnourished. Subsequently, the rate of liver cancers among those islanders increased sharply. The donated milk was probably to blame: recent laboratory research on rats has shown that rats briefly exposed to the substances aflatoxin tend to develop liver cancer when fed casein, a milk protein. This result is relevent because              

A:  in the tropics, peanuts, a staple of these island residents, support a mold growth that produces aflatoxin.

why select A?

哪位牛人给指点一下？ 应该是irrelevant吧。

liver cancer ＝ fed casein （in milk）+  exposed to aflatoxin （in peanuts）

hence ,choice A is the correct answer