Which of the Following Would Not Limit the Extent of a Firm's

Which of the following would not limit the extent of a firm's vertical integration?

A) the managers' bounded rationality
B) a large minimum efficient scale of producing inputs relative to the firm's input requirements
C) the fact that the quality of inputs is easily determined at the time of purchase
D) many interchangeable suppliers of the firm's inputs
E) high transaction costs of contracting with resource suppliers