[求助]who can help me? thanks!!

tchanu2003

441. No less an authority than Walter Cronkite has reported that half of all Americans nevere read a book.
A. No less an authority than
B. Nonetheless an authority
C. Nevertheless authoritarian
D. Not less an authority than
E. An authority not less than

The answer is D. I know " no more than" and "no less than". What is the difference between " no less ... than" and "not less ... than", as well as between " no more ... than" and " not more ... than"? Thanks!