Which of the following is one of the conditions indicating that using a single plantwide factory overhead rate may cause product cost distortions?

a$.$ Differences between production for one period compared to production in the next period

b$.$ Differences among total budgeted overhead and total budgeted allocation base amount

c$.$ Differences in production department factory overhead rates

d$.$ There are no specific conditions indicating that a single plantwide factory overhead rate may cause product distortions