Question

We had dinner in ______ most expensive restaurant in town.
A. A
B. An
C. The
D. No article

Answer 1

Hint:Somebody or something may also be defined by saying that they have more of a certain quality than any other of their kind. We do this by using superlative adjectives formed by adding-est at the end of the adjective and placing the adjective before it or placing the most before the adjective, e.g.
We use a superlative to mean that the greatest part of a group is a thing or individual. We use a certain article when we use a superlative adjective before the noun, since there is only one (or one group) of items that we are talking about.

Complete answer:
There is one restaurant which is most expensive in town, and because it's clear to the listener which one we mean, we usually use 'the':-
We had dinner in ‘the’ most expensive restaurant in town.
Noun (subject) + verb + the + superlative adjective + noun (object).

Lets see other options :-
A :- A is used before words that begin with consonant sounds. Thus this option is wrong.
An :- an is used before words that begin with vowel sounds. Thus this option is wrong too.
The :- Before superlatives, the definite article 'the' is used. Here,' most expensive' is the adjective's superlative form. The correct answer is, therefore,' the'.
No article :- no article is used for indefinite, uncountable nouns thus this option is wrong.

Thus option C is the correct answer.

Note:In English, most superlatives, including the examples above, can be formed by adding -EST to an existing adjective. (You also change the "-y" to a "crazy" for adjectives ending in "y" such as I before you add the -EST at the end.)
There are irregular superlative forms in some adjectives, which do not obey the rules, such as far ("farthest").