Answer: This sentence is a complex sentence.
Step-by-step explanation:
A complex sentence is made up of an independent clause and one or more dependent clauses. In this sentence, "Dr. Seuss is a famous author" is the independent clause and "who is primarily known for writing children's books" is the dependent clause. The dependent clause modifies or gives more information about the independent clause, providing more details about the subject, in this case, Dr.Seuss.