Which One of the Following Variances Is of Least Significance

Which one of the following variances is of least significance from a behavioral control perspective? (CMA adapted)

A) Unfavorable materials quantity variance amounting to 20% of the quantity allowed for the output attained.
B) Unfavorable labor efficiency variance amounting to 10% more than the budgeted hours for the output attained.
C) Favorable materials price variance obtained by purchasing raw materials from a new vendor.
D) Fixed factory overhead volume variance resulting from management's decision midway through the fiscal year to reduce its budgeted output by 20%.