Answer:
The correct answer is: They are arguing because her sister-in-law wants to sell the house.
Step-by-step explanation:
Mr. Tibbets's sister-in-law, Tabitha, wants to sell the house, but Ms. Tibbets doesn't want to sell it. Her sister-in-law, Tabitha Turner owns the land with the pool on it and her intention is to take the property down, build some houses, and earn some money.
This property is meaningful to a fifth-grader Ben Moroney, who wants to protect the natural habitat where live the endangered spade-foot toads. He tries to help his science teacher, Mrs. Tibbets, to save the property, by trying to convince her sister-in-law to keep the property.