The sentence that correctly uses hyphenation conventions is:
The contractor kept the load-bearing wall.
Hyphens are correctly used in compound adjectives that precede a noun (e.g., "load-bearing").
The other options contain errors in hyphenation:
- "The boy made everyone laugh with his quick-wit." should be "quick wit" without the hyphen.
- "The two faced-woman was unliked by others." should be "two-faced woman" with a hyphen between "two" and "faced."
- "The smile appeared under the salt-and pepper mustache." should be "salt-and-pepper mustache" with a hyphen between "salt" and "pepper."