阅读：宇宙与航天科普文章 — 英语词汇题
题目
根据句意及首字母或中文提示补全本单元词汇。1. The moon is a natural s________（卫星）of the earth. 2. Astronauts travel in a r________（火箭）to space. 3. Scientists study the u________（宇宙）to learn about stars and planets. 4. A p________（行星）like Mars goes around the sun.