Final answer:
The sentence 'I drew an illustration for a poem that was written by Robert Frost' is a complex sentence.
Step-by-step explanation:
The sentence 'I drew an illustration for a poem that was written by Robert Frost' is a complex sentence. It contains an independent clause 'I drew an illustration' and a dependent clause 'that was written by Robert Frost'. The dependent clause cannot stand alone as a complete sentence.
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