单选题

　　[完成句子]The importance of particular metals in the human diet has been realized within the past few decades， and the idea that geology might be related to health has been recognized for a number of elements such as iodine， zinc and selenium. For example， soils with low iodine contents produce crops， and animals deficient in iodine. A lack of iodine in the human diet leads to some serious diseases.

　　Some serious diseases is connected with deficiency of __________.

　　A、industrially polluted soils

　　B、the element of iodine

　　C、rock and soil chemistry

　　D、the persistence of heavy metals