根据句意首字母或汉语提示完成单词。
L____ travels much faster than sound.
Some spacecrafts have gone b____（在……之外）the solar system.
Scientists have discovered many other planets in the u ____.
The earth is a p ____ and we live on it.
The Mars is a _____ (行星)in the solar system.
You should       (交流) with your friends more often.
How many       (组) are there in your team?
We should protect our       (环境) well.