The difference between the group means in a pretest-posttest control group experimental design can ...

The difference between the group means in a pretest-posttest control group experimental design can be tested for statistical significance most precisely by
 
  a. analysis of variance of the groups' means on the posttest.
  b. separate t-tests of the prepost difference for the experimental and for the control group.
  c. analysis of covariance on the groups' posttest means with pretest as the covariate.
  d. analysis of variance of the mean changes from pre- to posttest for the two groups.

Ques. 2

Which of the following is not a characteristic of an experiment in its simplest form?
 
  a. A dependent variable is manipulated.
  b. All variables except the independent variable are held constant.
  c. The effect of manipulating the independent variable is observed.
  d. Extraneous variables are controlled.