In which sentence is the underlined prepositional phrase an adverb phrase?

light from far away galaxies scientists figure out what stars are made of.
the milky way is one of many star systems.
the world’s largest telescope can be found at the hawaiian observatory.
astronomers discovered a quasar 12 billion light years away in 1991.

in which sentence is the underlined prepositional phrase an adverb phrase?

light from far away galaxies scientists figure out what stars are made of.
the milky way is one of many star systems.
the world’s largest telescope can be found at the hawaiian observatory.
astronomers discovered a quasar 12 billion light years away in 1991.

D). Astronomers discovered a quasar 12 billion light years away in 1991.

Explanation:

A Prepositional phrase comprises of a preposition followed by an object(that could be a pronoun or noun, etc. and it's modifier. This phrase usually functions either as an adjective or as an adverb. As per question, the sentence among the given options that carries a prepositional phrase functioning as an adverb phrase is displayed through option D as it contains the prepositional phrase('away in 1991') that modifies the verb 'discovered' and also answers the question 'when?'. Therefore, option D is the correct answer.

alone =having no one else present.

an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.