Исправьте ошибки в предложениях.
1. He is the oldest student in his group.
2. You are taller then me.
3. My car is better than his.
4. It is one of the most beautiful lakes in the world.
5. These flowers are more cheape than those ones.

He is the oldest student in his group.  (ошибок нет)

You are taller than me.    (Тут нужно вместо then, вставить-than(чем).

My car is better than his. (ошибок нет)

It is one of the most beautiful lakes in the world. (правильно)

These flowers are cheaper than those ones. (cheap - это односложное слово и следует использовать окончание сравнительной степени)