填空题
Oil Thursday afternoon, Mrs. Clark got dressed for going out. She took her handbag, with her (AA) （） inside it and left her house, pulling the door behind her to lock it. (AB) （）she came home and got into the house with her key. At once she smelled cigarette smoke. Cigarette smoke in her house How Had anybody (AC)（）in while she was at the club She checked the back (AD) （） and all the downstairs (AD) （）. They were all securely fastened. There was no sign that anyone had forced his way in. But one thing was certain: (AE) （）had been smoked in her house that afternoon.
What was certain according to the passage