[单选] ① She bought a digital camera online so that she would save a lot of time．② They set out early so that they might arrive in time．③ He worried so that he couldn"t sleep．④ Woodman and his friends wanted to "go pro" so that they could get photos or videos of themselves surfing．⑤ You must speak louder so that you can be heard by all．⑥ It was very cold， so that the river froze．以上哪几个句子是目的状语从句？