Mock Question

Which TWO of the following factors should be considered before investigating an adverse material usage variance?

Worldwide increase in cost of raw material
Tolerance limits
Interrelationship with adverse labour rate variance
Cost involved in the investigation

Answer are 2 and 4.
My question is that if favorable labor efficiency variance would have been in answer so would it have been correct? As labor might have worked more quickly due to which they have wasted material.