Incomplete question. However it is inferred that question can be answered generally speaking.
Answer:
c. the accessibility of cheap cotton.
Step-by-step explanation:
Remember, selling price is a function of cost. Therefore, a $5 T-shirt may to a very large extent be affordable by most persons in the United States, because of the accessibility of cheap cotton in the country.
This access to cheaper raw material may increase the number of manufacturers in the country; resulting in a fair price for T-shirts due to competition among manufacturers.