Which sentence uses the superlative form correctly?

Question

A.
The book on quantum physics is most dull than the book on sports.
B.
The expression on my father's face was the most grim I had ever seen.
C.
Sheila Kellar is considered by many to be the haughtiest girl in school.
D.
Julius, my younger brother, is the most tall student in the ninth grade.

Answer 1

The sentence that uses the superlative form correctly is:

C. Sheila Kellar is considered by many to be the haughtiest girl in school.

The other sentences have grammatical errors related to the use of superlatives.