The Federal Trade Commission is being asked to explain why the rental car industry shouldn’t have to live by the same rule that requires auto dealers to fix vehicles under recall notice before they can be sold. Safety groups say most business travelers or those renting cars for long trips don’t know whether the vehicle they pick up at the rental lot has been the subject of a recall, posing a potential safety threat. The issue has taken on more significance this year following a series of safety recalls by Toyota Motor Co. and several large recalls involving other automakers.