Trainers at the CBR Corporation evaluated a customer service training program by assessing the customer service skills of all participants at the beginning of the program, using a role-playing exercise. After the training was completed, the customer service skills of all participants were assessed again using the same exercise. Results indicated that participants' customer service skills improved significantly by the end of the training program. This is an example of which training evaluation design? Multiple Choice posttest only pretest/posttest time series pretest/posttest with comparison group pretest only