A famous Renoir had been stolen from a museum. Detective Earl Blackman was to work on the case. Everyone was in the dark before an art professor came to point out the false picture. So the museum even didn't know when the picture had been stolen. Thousands of people came to visit the museum every day. After long work, some art students were focused on. The five students who had made copies of the Renoir during the last six months were asked to bring their copies to the museum. The fifth student said she had sold her copy, which was later proved to be the one in the museum. She, however, could only remember the buyer was a man with the little finger on his left hand missing. Blackman went back and stayed in his office looking at all the pictures of known thieves. No success. The next afternoon, at about closing time, Blackman went to the museum to ask if the cleaning men were in the museum after everyone else had left. The director told him they had no cleaning man but six cleaning women. As the detective left the director's office, he saw five cleaning women. He stopped one and asked about her work. Then came the sixth cleaning woman. She was dressed just like the other women except the gloves on her hands which made her different. Blackman watched her for some time. When she came near, Blackman caught her. The woman cried out in a man's voice, "What was that?" Blackman was more sure. Blackman caught the cleaning woman because of   _  .
the glove the clothes her sex her work