Which of the following statements is true of solomon four-group evaluation design?
a. relative to the other evaluation designs, it is more economical and takes less time to conduct.
b. it is an evaluation design in which pre-training outcomes are completely ignored.
c. it is mainly used by companies that are uncomfortable with excluding certain employees or that intend to train only a small group of employees.
d. it combines both pre-test/post-test comparison group and post-test-only control group design.