This is because the sound you make when you say x is ex thus using a but when you make the b sound it sounds like be.
Answer:
Agriculture is the art and science of cultivating the soil, growing crops and raising livestock. It includes the preparation of plant and animal products for people to use and their distribution to markets. Agriculture provides most of the world's food and fabrics.
B,makes more sense especially if you asked a question in the first paragraph!
