Fill in the blank with the most appropriate word.
It was ____________ hot in the train.
An adverb is a word or phrase that qualifies or changes an adjective, verb or another adverb, to express a relation of a situation, cause etc.
The correct answer is D)terribly as it describes the extreme condition.
Options A, B, and C are wrong as 'extreme' and 'intolerable' are adjectives and 'worse' indicates something done less skilfully.
It was terribly hot in the train.