对中国封建制度的建设最具成就的时期是①秦汉 ②隋唐 ③宋元 ④明清
A:①②
B:①③
C:②③
D:①④
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-- What do you think of Bill?
-- I used to think that he ____ (be) an honest boy.
60°,一个半径为1的小球放在支架上,则球心O到点P的距离是( )