The first movie I watched was Tom and Jerry. Then I came to Snoopy. I couldn't always

understand all the lines, _________ I used the subtitles to help me. In this way I learnt many everyday expressions that I couldn't find in my textbooks.

向各位老师请教一下这段话横线部分填什么词？答案是but，但我觉得so也可以啊，请问

1. so是否也行  

2. but的合理性在哪里？

谢谢各位老师！