Life in the city is … challenging for the lazy.

Analyze the question: The blank comes before the adjective "challenging". We need a phrase that modifies an adjective and means "excessively".

Concept: "much too" vs "too much"

• Much too + adjective/adverb means "excessively" (e.g., The soup is much too hot.)
• Too much + noun means "an excessive amount" (e.g., There is too much salt in the soup.)
• So much / very much are usually used with verbs or nouns, not directly before an adjective (e.g., I like it very much.)

Solution: The word after the blank is "challenging", an adjective. So we need a phrase that intensifies an adjective:

• A. too much challenging: incorrect, because "too much" goes with nouns or verbs
• B. so much challenging: incorrect, because "so much" doesn't modify adjectives this way
• C. very much challenging: incorrect, because "very much" doesn't go directly before an adjective like this
• D. much too challenging: correct, because "much too" modifies the adjective "challenging"

Complete sentence: "Life in the city is much too challenging for the lazy."

Tip: Remember the order: "much too" comes before an adjective (much too big, much too late), while "too much" comes before a noun (too much rice, too much noise). Ask yourself: "What follows the blank, an adjective or a noun?"