题目

 ---Peter, where did you guys go for the summer vacation?    ---We _______ busy with our work for months, so we went to the beach.   A. were                           B. had been                   C. have been                 D. will be 答案：B.科学家用含有mC的二氧化碳来追踪光合作用中的碳原子,这种碳原子的转移途径是  A、二氧化碳一叶绿素一ADP   B、二氧化碳一叶绿体一ATP C、二氧化碳一乙醇一糖类    D、二氧化碳一三碳化合物一糖类