Explanation:

- Option 1: Can be negative

- Average revenue (AR) represents the revenue per unit sold.

- Since it is derived from dividing total revenue by quantity, it cannot be negative unless units are sold at a negative price, which is unrealistic.

- Option 2: Cannot be negative

- Average revenue is typically non-negative because prices and sales quantities are non-negative.

- Option 3: Is zero when TR is zero

- Total Revenue (TR) is zero when no units are sold. Therefore, AR would also be zero as revenue per unit from zero sales is zero.

- Option 4: Both (b) and (c)

- Combines the non-negative nature of AR and the condition when TR is zero.

Correct Answer: Option 4: Both (b) and (c)

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