题目

已知集合A={ (x，y)|x，y为实数，且x2+y2=l}，B={(x，y) |x，y为实数，且y=x}，  则A ∩ B的元素个数为（    ） A、0     B、1    C、2     D、3 答案：She returned home from the office, only ________ the door open and something missing. A. finding B. to be found  C. to find  D. found