题目

已知矩形的两条对角线的夹角为60°，对角线长为15，则矩形的较短边长为 ．   答案：7.5  Without facts，we can’t form a correct opinion，for we need to have actual knowledge______our thinking. A.which to be based on                                     B.which to base on C.on which to base                                           D.which to base