Answer:
Although John's boat was at the landing, the boy's son-in-law was nowhere in sight.
Explanation:
The correct form of the word used in the sentence is the third option which is son-in-law.
A son-in-law is the husband of one's daughter or son. The other word forms are incorrect because the plural form of son-in-law is son-in-laws and it is not available in the option.
No form or tense of the word son-in-law has an apostrophe separating any of the words.
