Answer:
b) Participial phrase.
Explanation:
A participial phrase is a phrase or groups of words that seems or looks like a verb but acting as an adjective. It also modifies the noun in that sentence. It thus provides 'extra' details about the noun, giving more details and making it more 'rich'.
In the sentence -
Frustrated by the woman's response, the border guard repeated his question
the sentence contains a participial phrase "frustrated by the woman's response". It acts as an adjective, modifying the noun but seems like a verb/ action. it also gives us the reason why the border guard had to repeat his question.
