________ a car reaches the end of its life, it is taken apart and any part that can be reused is sold off．

1. A.
   As
2. B.
   Once
3. C.
   While
4. D.
   With

_____ a car reaches the end of its life, it is taken apart and any part that can be reused is sold off.

A. Until　　　　 B. Once　　　　　 C. Since　　　　 D. While