【简答题】设A={1,2,3,4,5,6},定义A上的二元关系: R 1 ={(1,1),(2,2),(3,3),(4,4),(5,5),(6,6)}∪ {(1,4),(2,3),(2,6),(3,2),(3,6),(4,1),(6,2),(6,3)}, R 2 ={(1,2),(2,1),(2,2),(3,3),(4,4),(4,5)}.
【简答题】A.It lacks the necessary background information. B.The man should find the proper subject to research firstly. C.It will be finished in a short time. D.The man doesn't know how to carry it on.