Which of the following statements is (are) true?
i. if labor and capital are perfect substitutes in production, the isoquant is a straight, downward-sloping line.
ii. if a company needs to use inputs in fixed proportion such that the capital to labor ratio is always 2, the firm's isoquants are l-shaped.
iii. if the production function is given by q = min(14, 7), the firm can produce, at minimum, 21 units of output.

a. iii
b. i and ii
c. i
d. i, ii, and iii