A makes the most sense because the the people shift to systematic agriculture and can grow crops and farming products such as rice, beans, corn, and squash near them, which saves them amount of time they spend by searching/hunting animals. Also, it becomes more convenient for them to store some crops for the winter.
B does not make sense because this answer is stating that people began hunting and gathering food, while the question is asking why people <u>stopped </u>living as nomadic hunter-gathers.
C does not make sense because pottery is not related to them searching/growing food.
D does not make sense because flooding will only make it difficult for the people to find food.
