题目

“Sesame Street” has been called “the longest street in the world”. That is because the television program by that name can now be seen in so many parts of the world. That program became one of American’s exports soon after it went on the air in New York in 1969. In the United States more than six million children watch the program regularly. The viewers include more than half the nation’s pre-school children, from every kind of economic(经济的), racial(种族的), and geographical group. Although some educators object to certain elements in the program, parents praise it highl 火星中存在一种含铁元素的矿物，化学式为KFe3(SO4)2(OH)6，其中Fe元素的化合价为 [　　] A． ＋2 B． ＋3 C． 0 D． －2