13．根据下面的对话内容，在横线上填入恰当的句子，使对话通顺，结构完整． A：Hello，Cindy!（66）How are you？ B：I'm fine，thanks． A：（67）What's your favorite subject？ B：My favorite subject is science． A：（68）Why do you like science？ B：Because it's difficult but interesting． A：（69）Who is your science teacher？ B：Mr．Lin is my science teacher．We like him very much． A：Oh，Mr．Lin．Today is Friday．It's Mr．Lin's birthday．I know he'll have a birthday party tonight． B：Let's go to his birthday party． A：（70）Good idea．．
