A researcher administers a critical thinking test to a group of employees in an organization. They are then made to go through an intensive workshop on critical thinking skills. At the end of the workshop, the critical thinking test is given again and a large improvement in test scores is discovered. This is an example of a control series design. nonequivalent control group design. one-group pretest-posttest design. Solomon four-group design.

c). one-group pretest-posttest design

Explanation:

'One-Group pretest design' is depicted as the research pattern in which the researcher examines the impact of an intervention or manipulation in the independent variable on the provided sample. Such a method includes only one research group and is primarily employed for examining behavioral changes post manipulation in the variable.

The given research exemplifies this 'one-group pretest-posttest design' as it involves a single group comprising of participants who would take part in the research and the impact of manipulation in the independent variable('going through an intensive workshop on critical thinking skills') on the participant's ability to think critically. This will allow assessing whether the workshop affected their outcomes or not. Hence, option c is the correct answer.