Which of the following should not be capitalized in titles?

In title capitalization rules, small words such as conjunctions, prepositions, and articles are typically not capitalized unless they are the first or last word in the title. This includes words like "of," "and," "in," "the," and "but." The rationale behind this is to give emphasis to the more significant content words—nouns, pronouns, adjectives, verbs, and adverbs—which convey the primary meaning and importance of the title.

Therefore, the choice that suggests small words like "of" should not be capitalized accurately reflects standard title capitalization practices, thereby making it the correct answer. Other options refer to major words that should indeed be capitalized, as they contribute to the overall clarity and impact of the title.