Ⅰ. 根据句意及首字母提示完成单词（10分）
1. He often does some e _______ in the laboratory.
2. She gave me an u _______ gift on my birthday party.
3. P_______ is a difficult subject to understand.
4. Everyone should o _______ the public rules!
5. She said she would t _______ to the USA the next year.
