There was time Chinese used foreign oil.A. /; whenB. a; whileC. a; whenD. /; while

网友回答

A. /; when
B. a; while
(答案→)C. a; when
D. /; while
解析：句意：有一段时间中国人使用外国的油。there was a time 历史上有一段时期。time 后接定语从句用关系副词when作连接词在从句中作时间状语。故选C。