Continue to use the example from Question 13: Suppose each product is randomly assigned to a process by a computer program, but some products get reassigned on the factory floor (for practical reasons). Let Zi denote the original assignment and Xi the actual process used to produce i. In a regression oni on Xi and W, OLS is: O a. Unbiased because the products were randomly assigned in the beginning 0 b. Unbiased as long as Zi is also included as a control variable 0 c. Potentially biased, but an IV regression using Zi as an instrument can be used to obtain a consistent estimator Q d. Potentially biased because Wi should not be included