he starts to do something.he won’t stop until it is finished. A．Though B．Since C

________he starts to do something，he won’t stop until it is finished.

A．Though                                             B．Since  

C．Unless                                                D．Once

试题答案

D　他一旦开始干一件事，不干完就决不罢休。once此处用作从属连词，表示“一旦”，引导状语从句。