Groups of words containing prepositions are called prepositional phrases. Keep in mind that prepositions will be words that demonstrate the connections between different components inside a sentence, and you'll never experience issues distinguishing prepositional expressions, for example after, in, to, on, and with.
Answer:
"During the long days,"
Explanation:
A prepositional phrase is a part at the beginning of a sentence that adds a prefix to the following statement.
i.e. without the words "During the long days," the sentence would infer a different conclusion (and change the tense!)