Final answer:
In Dr. Seuss's book, young Marco's imaginative journey occurs on a) Mulberry Street, which matches the title of the book and is located in New York City.
Step-by-step explanation:
The imaginative young Marco embarks on an adventure in Dr. Seuss's engaging book "And to Think That I Saw It on Mulberry Street".
The correct answer to the question about where Marco's imaginative journey takes place is a) Mulberry Street. This choice is directly supported by the title of Dr. Seuss's book.
Mulberry Street is an actual thoroughfare located on the Lower East Side of New York City, depicted in historical photographs as a bustling area filled with diverse activities and people which reflect the vivid scenery Marco envisions in his imagination during the story.