皮亚杰的儿童认知发展理论分期包括（）。

A.感觉运动期

B.持续发展期

C.具体运算期

D.形式运算期

E.运算前期

— I paid him 300 Yuan for the sneakers.  

— Oh.  he charged you too much. You _______ them with half money. [      ]

A.  could have bought    

B.  needn't have bought

C.  must have bought     

D.  wouldn't have bought