Final answer:
The absolute superlative of 'largo' is 'larguísimo,' with the spelling change involving the replacement of 'o' with 'u' before adding the superlative suffix '-ísimo' to maintain pronunciation.
Step-by-step explanation:
The absolute superlative for the adjective largo (meaning "long") in Spanish involves a spelling change. In its regular form, the adjective is simply largo. However, to express the absolute superlative, which amplifies the quality denoted by the adjective to its utmost extent, we typically add the suffix -ísimo to the stem of the adjective. Therefore, the absolute superlative form of largo would be larguísimo. Notice that the letter 'o' in the root form changes to 'u' in the superlative form (larguísimo) to maintain the proper pronunciation.