Why is the flexible$-$budget variance the same amount as the rate variance for fixed manulacturing overhead?

A$.$ There is sometimes an efficiency variance for fored overhead because managers can be more or less efficient in dealing with an amount that is fred regardless of the output level.

B$.$ There is always an efficiency variance for foxed overhead because managers can be more or less efficient in dealing with an amount that is fixed regardless of the output level.

C$.$ There is never an efficiency variance for foxed overhead because managers cannot be more or less efficient in dealing with an amount that is fred regardless of the output level.

D$.$ None of the above.