If the XYZ Company can sell 4 units per week at $10 per unit and 5 units per week at $9 per unit,the marginal revenue of the fifth unit is $5.

Marginal revenue is the change in total revenue that results from selling one additional unit.

From the given information, the company sells 4 units per week at $10 per unit, so the total revenue for selling 4 units will be 4 x $10 = $40.

When the company sells 5 units per week at $9 per unit, the total revenue for selling 5 units will be 5 x $9 = $45.

Therefore, the marginal revenue of the fifth unit is $45 - $40 = $5.

Hence, the statement is true and the answer is A.