Which is the correct answer? The role of the covariate is to: a. Compare variables of interest without a nuisance variable masking true differences. b. Reduce within-wroup error variance and help...

Which is the correct answer?

The role of the covariate is to:

a.  Compare variables of interest without a nuisance variable masking true differences.

b.  Reduce within-wroup error variance and help eliminate coonfounding variable bias

c.  To determine the predictive power of the independent variable using odds

d.  A & B