、Learning aims
1.Grasp the key words and key structures:
Planet,solar,none,environment,galaxy,,billion,universe,,light,beyond,alone,
entrance,prefer
2.Present perfect tense with just, already and yet.
3.Reading skill: To understand passages about space travel involving present perfect tense.
二、一）单词检测
1. The earth is a p ____ and we live on it.
2. Scientists have discovered many other galaxies in the u ____.
3. Scientists think that there has been life on Earth for m____ of years.
4. L____ travels much faster than sound.
5. A b____ is 1.000,000,000.
6. If you don’t want to go a____(单独) ,I’ll go with you .
