Including a nuisance variable as an independent variable in your experimental design

Including a nuisance variable as an independent variable in your experimental design
 
  a. is a mistake to be avoided
  b. can increase the sensitivity of the experiment
  c. is a type of manipulation check
  d. decreases the generality of the results

Question 2

A nuisance variable is
 
  a. the same as a confounded variable
  b. a second independent variable in an experiment
  c. one that is included even though it is not of theoretical interest
  d. Both b and c are correct.

Question 3

Matching may justified in an experiment if
 
  a. there is a variable that is highly correlated with the dependent variable
  b. it is feasible to present a pretest before assigning subjects to conditions
  c. Both a and b are true.
  d. Matching is always justified.