一般过去时与过去完成时的区别 — 英语词汇题
题目
完成句子：根据括号内动词的适当形式填空。1. Before Admiral Zheng He set out on his seventh voyage in 1430, the emperor ___ (order) him to improve the sea maps used on earlier journeys. 2. The sailors were tired because they ___ (sail) across the ocean for three months before they saw land.