Answer:
"having been long enclosed"
Explanation:
A participle is a verb that ends with the suffix -ing, -ed, -en, -d, etc.
It can serve the function of an adjective by modifying the noun or pronoun in the sentence.
A participial phrase are group of words that are made up of a participle and nouns, pronouns or noun phrases which serve the function of being direct objects, indirect objects or action complements.
