Select the most appropriate article to fill in the blank. If no article is needed, select 'No article required'.
_______ best thing about being old is that you tend to get the respect of all and sundry.

Correct option is C

The correct option to fill in the blank is (c) The.
Explanation:
The adjective best is the superlative degree of good. Superlative adjectives are generally preceded by the definite article the because they refer to one thing as the highest or most outstanding within a group.
Thus, the correct sentence is:
The best thing about being old is that you tend to get the respect of all and sundry.
Example:
· The highest mountain in the world is Mount Everest.
· She is the best player on the team.
Why other options are incorrect:
· (a) A: Incorrect because superlative adjectives normally take the, not a.
· (b) An: Incorrect for the same reason.
· (d) No article required: Incorrect because best requires the in this context.
Information Booster:
Use the before:
· Superlative adjectives: the tallest, the strongest, the most beautiful.
· Ordinal numbers: the first, the second.
· Unique objects: the Earth, the Sun, the Moon.
Exception:
When a superlative is used merely for emphasis rather than comparison, a may occasionally be used.
Example:
That was a most interesting lecture.