Adjective phrase is a group of words that are used to describe a noun. In this sentence the phrase "from our vacation" describes the noun and subject of the sentence photographs. Therefore, you are correct the answer is C.
The adjective phrase in the sentence "We printed photographs from our vacation and gave them to friends" is "from our vacation." This phrase describes the noun "photographs" by specifying where they are from. Thus, option C is the correct answer.
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