Choose the option that fills in the blank with the most appropriate word:
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 C)then as it describes a time period.
Options A, B, and D are wrong as they indicate the present moment, a place nearby, and a place at a higher level respectively.
The then president chose to go to war.