题目

在①正三角形、②正方形、③正六边形中能密铺平面的是（） A . ①②③ B . ②③ C . ①③ D . 以上都不对 答案：A—Can you tell me if Tom has finished his homework?—I've no idea. He ________ it this morning.A．has being doing B．had done C．is doing D．was doing