用两根绳子吊起—重物，使重物保持静止，若逐渐增大两绳之间的夹角，则两绳对重物的拉力的合力变化情况是                                                 (      )                                                                                     A．不变    B．减小　　C．增大   D．无法确定

A.不变                B.减小                C.增大              D.无法确定

A.不变                                                                   B.减小

C.增大                                                                   D.无法确定

A.不变              B.减小                 C.增大                  D.无法确定