All of the Following Statements About the Constant Gross Margin

All of the following statements about the constant gross margin percentage net-realizable method are true EXCEPT

A) all products have equal gross margin percentages.
B) it is based on a tenuous underlying assumption.
C) the gross margin percentage remains the same regardless of the different amounts of separable costs.
D) the gross margin is calculated by deducting all separable costs from revenue.
E) some products may receive negative allocations of joint costs.