题目

At a meeting, a well-known speaker lifted up a bill of 20 dollars before starting his speech. Facing 200 people, he asked, “Who wants this 20-dollar bill?” A great many hands were put up. Then he continued to say, “I intended to give it to any one of you, but allow me to do a thing before giving it to you.” Suddenly he crumpled （揉）it into a round mass. Then he asked, “Who wants it? ” Still some hands were lifted up. He asked again, “Well, how could it be if I do it like this?” he threw the bill onto the ground, stepped on it and twisted it. As he picked it up, the 下列图形中，是轴对称图形而不是中心对称图形的是（    ）A．圆      B．正方形     C．矩形     D．正三角形