It isnt just that the level of education of this school is high. Its that its also been consistent for years. k

A. It isn't fair to deny that this school is successful, as it has had the same high standards for many years now. 

B. The standard of education is not high in this school, but at least all the students are at the same.

C. The level of education in this school, which is usually quite high, shows only slight variations from year to year.

D. Not only are the standards of education good in this school, but it has maintained those standards over the years.