because引导原因状语从句 — 英语填空题
题目
用 because 把下面的两句话合并为一句，使句意通顺、语法正确，第一个空填连词，第二个空填从句（主谓结构完整）。Guide dogs are very helpful. They can help blind people because they are well trained (经过良好训练). 合并后：Guide dogs are very helpful ___ they ___ well trained.