并列连词so的用法说明
so用作并列连词时主要表示结果，意为“因此”“所以”。如：
I was tired, so I went to bed earlier. 我累了所以早点睡了。
He took my shoes, so I couldn’t leave the house. 他把鞋拿走了，我出不了门。
It was very cold, so we had to wear warm clothes. 天气很冷，所以我们得穿暖和的衣服。
按英语习惯，表示结果的so不能与表示原因的because套用，在使用时只能保留其中的一个。如：
那是一个难题，所以我最后才回答。
误：Because that was a difficult question, so I answered it last.
正：That was a difficult question, so I answered it last.
正：Because that was a difficult question, I answered it last.