根据我国《建设工程施工合同(示范文本)》规定，更换发包人代表，发包人应当提前以书面形式通知承包人，提前的期限至少是( )。

A．24小时

B．72小时

C．7天

D．14

_____ learn English well, we must listen to the teacher carefully.[ ]

A. So as to    

B. In order to    

C. So that    

D. In order that