Here's a step$-$by$-$step solution to the problem:The question asks which of the four statements is true regarding service department cost allocation. Let's analyze each statement:Statement $1$: This statement is incorrect. While sales dollars might be a factor, it's not superior to other allocation bases. Other factors like service usage or activity levels are often more accurate.Statement $2$: This statement is correct. Performance evaluation should focus on the service department's ability to manage its own costs, not on shifting blame for variances to other departments.Statement $3$: This statement is correct. Charging actual fixed costs proportionally to service usage is a fair and accurate method of cost allocation.Statement $4$: This statement is correct. Separating fixed and variable costs allows for more accurate cost allocation and better management control.Therefore, statements $2,3,$ and $4$ are true. However, the options only offer combinations of two statements. The most accurate option is "Both statements $2$ and $4$ are true".Answer: Both statements $2$ and $4$ are true.