In all forms of imperfect competition, the average revenue curve facing the individual slopes

upward
downward
parallel to X-axis
vertically

The correct answer is: B. downward.

In all forms of imperfect competition, the average revenue curve facing the individual firm slopes downward. This is because the firm can charge a higher price for its product if it produces a smaller quantity. As the firm produces more, the price it can charge will fall, because there will be more competition from other firms.

Option A is incorrect because the average revenue curve facing the individual firm slopes downward, not upward.

Option C is incorrect because the average revenue curve facing the individual firm is not parallel to the X-axis. It slopes downward.

Option D is incorrect because the average revenue curve facing the individual firm is not vertical. It slopes downward.