Ifanythingshouldhappen,thenearestpersonhecouldcontactby...

问题详情：

If anything should happen, the nearest person he could contact by radio , _____ there was a ship nearby, would be on an island 885 miles away.

A. until         B. when           C. once             D. unless

【回答】

D

知识点：连词

题型：选择题