Fill in the blank with the most appropriate word.
The correct option is B 'killed'.
A verb is used to express an occurrence, action, or state. It is the grammatical center of the predicate in a sentence. An auxiliary verb is a verb that is used in the formation of tenses, moods, tones, etc. Option B is correct as 'was' indicates the use of killed.
The other options are wrong as no other tense can be used here.