1. Only under special circumstances, (学生才被准许提前毕业).
2. It has been proved that (我们的肤色取决于遗传).
3. No other reproduction in any form is permitted (未经出版社书面同意).
4. The environmental effect of this new factory (完全可以从周围的田地和河流看出来).

答案：
1. are students permitted to graduate in advance
2. the color of our skin is due to heredity
3. without written permission from the publishing house
4. is most clearly observable in the surrounding field and river