状语从句 Several weeks had gone by _____ I realized the painting was missing.中间的空为什么用before 而不用when?

状语从句 Several weeks had gone by _____ I realized the painting was missing.中间的空为什么用before 而不用when? several weeks ago 换现在完成时,是several weeks before还是for several weeks In the past several weeks,many cities in China have been suffeing from heavy fogs.想问,in the past several weeks 不是一个过去时态的时间状语吗?为什么用现在完成时呢? 状语从句, 状语从句 She had several weeks sewing.She had several weeks to sewing.哪个对简单说明理由 什么是状语,什么是状语从句? 目的状语从句,结果状语从句. 关于定语从句状语从句什么是定语从句状语从句 定语从句状语从句练习 宾语从句和状语从句 什么是状语从句 宾语从句 请帮我把这句话改成状语从句:(Having been trained)for weeks,she could drive the bus.( ),she could drive the bus. 状语从句的用法 时间状语从句讲解 时间状语从句讲解 什么是时间状语从句 状语从句是什么意思