In sentence 14, the correct change to make is insert "also" after "and". The correct answer is option D.
By inserting "also" after "and", the sentence will read: "Jen's parents are owners of the Birdsall's house and also the biggest house on the block."
This change improves the clarity and flow of the sentence by adding the word "also" to show that Jen's parents are not only the owners of the Birdsall's house but also the owners of the biggest house on the block. Without the word "also", the sentence could be interpreted as Jen's parents being only the owners of the Birdsall's house, not necessarily the biggest house on the block.
Another potential change that could be made in sentence 14 is option A: change "big" to "biggest". This change would make the sentence read: "Jen's parents are owners of the Birdsall's house and the biggest house on the block." This change emphasizes that the house owned by Jen's parents is the largest one on the block, providing additional information about its size. However, it's important to note that this change is a matter of style and emphasis, and both options A and D could be considered correct depending on the intended meaning and emphasis of the sentence.