1. Only under special circumstances, (學(xué)生才被準(zhǔn)許提前畢業(yè)).
2. It has been proved that (我們的膚色取決于遺傳).
3. No other reproduction in any form is permitted (未經(jīng)出版社書(shū)面同意).
4. The environmental effect of this new factory (完全可以從周?chē)奶锏睾秃恿骺闯鰜?lái)).

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
?