Suppose that the long-run industry supply in the production of synthetic fabrics is perfectly elastic. Which of the following statements is then true?
选项：

A: The marginal cost curve of each synthetic-producing firm is horizontal.
B: The existence of profit within the industry will not draw new firms into the market.
C: The long-run industry supply for synthetics is horizontal.
D: The long-run industry supply for synthetics is upward sloping.