Answer:
d. Stratified Sampling
Explanation:
Stratified Sampling is a form of sampling in which the researcher selects a population sample based on a demographic factor or strata such as race or gender. From the different strata, a random sample is then made such that each group or subpopulation is represented in the final sample.
It should be noted that retaining the percentages while selecting a randomized sample is essential to stratified sampling.
Hence, in this case, when the researcher obtains a list of all enrolled freshmen, manipulates the list so that females appear twice as often as males, and then selects from this list, this is an example of stratified sampling