The sentence: "Frank got maps for the Saturday hike to Nelson Park which was a great idea." is a phrase and the phrase "which was a great idea." functions as the subject complement.
This refers to the group of words that acts as a grammatical unit in a given sentence.
Hence, we can see that The sentence: "Frank got maps for the Saturday hike to Nelson Park which was a great idea." is a phrase and the phrase "which was a great idea." functions as the subject complement.
Read more about subject complement here:
https://brainly.com/question/1922820
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