1. 如果黑板就是浩淼的大海，那么，老师便是海上的水手。

2. 希望源于失望，奋起始于忧患。

3. 别在树下徘徊，别在雨中沉思，别在黑暗中落泪。

4. 柔和的阳光斜挂在苍松翠柏不凋的枝叶上，显得那么安静肃穆。

5. 生活的海洋并不像碧波涟漪的西子湖，时而平静如镜，时而浪花飞溅，时而巨浪冲天。

6. 当你身临暖风拂面，鸟语花香，青山绿水，良田万顷的春景时，一定会陶醉其中。

7. 倘若希望在金色的秋天收获果实，那么在寒意侵人的早春，就该卷起裤腿，去不懈地拓荒、播种、耕耘，直到收获的那一天。

8. 生活是蜿蜒在山中的小径，坎坷不平，沟崖在侧。

9. The arguer may be right about …, but he seems to neglect（fail） to mention（take into account）that fact that…

10. As opposed to（Contrary to）widely（commonly/generally） held（accepted）belief（ideas/views）,Ibelieve（arguethat…）.

11. Onthesurface（Atfirstthought）,it（this）mayseemasound（anattractive）suggestion（solution/idea）,butcarefulweightingonthemind（oncloseranalysis/onsecondthought）,wefindthat...

12. Itwouldbepossible（natural/reasonable）tothink（believe/taketheview）that…,butitwouldbeabsurd（wrong）toclaim（argue）that…

13. In all the discussionanddebateover…,one important（basic）factis generallyoverlooked（neglected）.

14. Too muchemphasis

15. From sth./what one has done, he can derive profits as follows.

16. Sth., if made the best/the worst of, will bring some distinct advantages/disadvantages to our social development/ones growth.

17. Sth. is expected to do a lot of benefit/threat/harm to sb./sth. else.

18. sth. will enrich/endanger/influence ones life in more than one aspect.

19. Some good/bad/unexpected effects come of what we have done/sth. done in

20. There are several reasons/causes/factors for the changes/increase/decline/growth in

希望这些中心句能满足你的需求。如果有更多具体主题或需求，请告诉我。