谈论太空探索与航天成就 — 英语词汇题

根据句意及首字母提示补全单词，完成与太空探索相关的句子。1. China has sent several s________（宇宙飞船）into space since 2003. 2. An a________（宇航员）must be healthy and well trained. 3. The satellite goes around the Earth in a fixed o________（轨道）. 4. Scientists hope to find life on other p________（行星）.