—What are they used for, Michael?        

—You can change the style of your shoes and make the shoes         from casual to dressy.            [ ]

A. to go

B. going

C. go

宁波轨道交通1号线、2号线建设总投资253.7亿元，其中253.7亿用科学计数法表示为

A．253.7×10⁸

B．25.37×10⁹

C．2.537×10¹⁰

D．2.537×10¹¹