题目

It was five o’clock in the afternoon _____ they climbed up to the top of the mountain.A. sinceB. when C. ThatD. until   答案：B此句为一主从复合句。when引导状语从句；若看作强调结构,应在five前加at。  判断对错 相邻两个自然数相差1． (　　)