A researcher is interested in whether using mental imagery can help people remember specific details when given information. To conduct the experiment, the researcher selects the treatment group by placing numbered slips of paper in a hat and randomly selecting half of the numbers, making sure to mix the slips between each selection. Which component is missing from the researcher’s process?

The researcher did not use randomization to select the treatment and control groups.
The researcher did not randomly choose the participants for the experiment.
The researcher did not label the participants with numbers before placing the numbers in a hat.
The researcher did not use enough random selections to make the correct number of group