根据所给句子和汉语提示写出恰当的单词，每空一词。
【小题1】Protecting the ________________(环境) is our duty.
【小题2】Leo couldn’t stop __________________(思念) his parents when studying abroad.
【小题3】My mother took me to school when I was at p________________ school.
【小题4】A sparrow was ______________(死). Let’s bury(埋) it under the tree.
【小题5】Why not take a d___________ flight to Sydney? It is much faster.