词汇 ；根据句意和汉语提示写出单词，完成句子。
1. My cousin used to be very interested in ____________ (收集) postcards.
2. The dentist suggests that we should brush __________(牙齿) three times a day.
3. He lost his iPad last ___________(星期三). He was very sad.
4. Armstrong joined the navy in 1949 and served as a _______ (飞行员) for three years.
5.___________ (比较) with life on the Earth, life on Mars would be better in some ways.