Correct answer only ! which of the following words in an adverb?

The correct answer is: a) históricamente.

Explanation:

Adverbs are the kind of words that modify and enriches the meaning of the verb. There are many type of adverbs, but the most common ones are the adverbs of place, time, manner, etc.

In Spanish, there is a simple technique of making adverbs of manner by adding the suffix -mente to a word.

inteligente + mente = inteligentemente

triste + mente = tristemente

When the adjective we want to make an adverb of ends in -o (male) and -a (female), we always take the female form to make an adverb.

rápido/a + mente = rápidamente

último/a + mente = últimamente

That is the case with this example, where we have the adjective

histórico/a + mente = históricamente

...meaning historically.