- An adverb is a word or set of words that modifies verbs, adjectives, or other adverbs. They answer questions such as how, when, where, why, how often, how much etc.
Option A) just is an adverb used to indicate a very recent occurrence.
Option B) before is an adverb used to indicate a time prior to the specified time.
Option C) always is used to indicate 'at all times'
Option D) yet is used to indicate something that has occurred or not occurred so far or thus far.
The given sentence talks about 'they were' and very friendly'. The best adverb that can complete the sentence is 'always' i.e option C) since the other words do not meaningfully complete the sentence.