The correct answer is D. John and Mary's house has a large front yard.
Explanation:
In English language, one of the most simple and common ways to show ownership is the use of the apostrophe ('), which is considered as a punctuation mark and therefore should be used following strict grammatical rules. According to grammar in most cases, it is necessary to add only the apostrophe (') followed by the "s" to show possession. However, when the noun that acts as an owner ends in "s" it is necessary to add only the apostrophe at the end of it.
On the other hand, when there is more than one owner which is the case presented the apostrophe and "s" should be added to each of them if each of them owns the object separately or just at the end of the last noun if they share the ownership. Considering this, the sentence that is correctly punctuated is "John and Mary's house has a large front yard", because in this case the both own the house and therefore it is necessary to add the apostrophe at the end of both, which means in Mary, also it is correct to use the apostrophe followed by the "s", because Mary does not already end in "s".
