单选题

　　1.[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