1. When did the world come into_______(形成)?
2. I’ve decided to ______（投资） in a new car.
3. The Tibetan antelopes are classed as a(n) _______（濒危）species.
4. We have been trying every means to _______（保持） the balance of nature.
5. You should make good use of every _______ (珍贵的)minute to study.
