What Are the Two Main Reasons for Including Covariates in ANOVA

Multiple Choice

What are the two main reasons for including covariates in ANOVA?

A) 1.) To increase within-group error variance and 2.To reduce between-group error variance
B) 1.) To reduce within-group error variance and 2.) Elimination of confounds
C) 1.) To increase within-group error variance and 2) .To correct the means for the covariate
D) 1.) 1.To increase between-group variance and 2.) To reduce within-group error variance