Answer:
independent groups
posttest only
pretest/posttest
Step-by-step explanation:
Posttest-only and pretest/posttest are the two elementary structures for experiments with independent-groups designs.
A posttest only design is most useful when spontaneous behavior is required from the participants.
Pretest-posttest designs developed from the posttest only design to consider issues of assignment bias and allocation of the participants, as they can avoid selection effects.