Question

select the word that means an open or available position. representatives in the united states congress are elected for two-year terms. sometimes, though, a vacancy occurs before the term ends. the only way to fill it is by holding a special election.

Explanation:

The question asks for a word meaning "an open or available position". From the context, "vacancy" is used to describe a position that becomes open before a term ends and needs to be filled by a special election. So "vacancy" is the word that means an open or available position.

Answer:

vacancy