题目

Not only the twins but also their cousin __________ Japan for half a year, but __________ of  them can speak Japanese.     A. has gone to; either                                 B. has been to; either     C. has been in; none                                  D. have been in; none 答案：C6．为了预防碘缺乏疾病，主要防治措施是在食盐中加碘，这里的“碘”应理解为（　　）A．元素B．分子C．单质D．离子