First impressions are the most lasting. After all, you never get _______ second chance to make

_______ first impression.     [ ]

A. a; the          

B. the; the          

C. a; a              

D. the; a

由脑和骨髓组成（　　）

A．白质

B．灰质

C．中枢神经系统

D．周围神经系统