The quotations "gigantic black smokestack," "half-built factory pipe," and "mast of iron gymnasium apparatus, incomplete, confused and deformed" contribute to the text by conveying a sense of disarray and unattractiveness associated with the Eiffel Tower's construction. They suggest a negative perspective on its appearance and form, indicating that some observers viewed it as ugly or unsightly. Therefore, the most appropriate answer is:
d. They highlight how some people regarded the Eiffel Tower as hideous.