The correct answer is:
a. In a standard costing system, the Work in Process account is maintained exclusively on the basis of standard costs.
Explanation:
- **Standard Costing System**: This system uses standard costs to value inventory and record cost flows.
- **Work in Process Account**: In this system, it is maintained using standard costs, which helps in variance analysis (comparing standard costs to actual costs to determine variances).
Other options are incorrect because:
- **b and d**: Standard costs can be used with both process costing and job order costing.
- **c**: Journal entries in a standard costing system use standard cost data, not actual cost data.