The correct answer is:
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The phrase, "long and filled with frustrations", modifies the word: "wait".
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Further explanation:
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Let us examine the other answer choices.
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→Let us examine the first answer choice given:
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  The phrase "in the end" modifies the word "needed".
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   → This is incorrect; since "needed" is not a noun or pronoun. As such,  Â
      this answer choice given is incorrect; since the phrase "in the end" is       NOT an 'adjective phrase' that modifies the particular word: "needed",
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→ Let us examine the third answer choice given:
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The phrase "The wait was long" modifies the word "frustrations".
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   → This is incorrect. The phrase, "The wait was long" does not modify the noun "frustrations." Â
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→ Let us examine the final answer choice:
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The phrase "we needed" modifies the word "what".
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   → This is is incorrect.  The phrase "we needed" is NOT an "adjective phrase".Â
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