In Order to Test the Effectiveness of a Drug Called

Multiple Choice

In order to test the effectiveness of a drug called XZR designed to reduce cholesterol levels,9 heart patients' cholesterol levels are measured before they are given the drug.The same 9 patients use XZR for two continuous months.After two months of continuous use,the 9 patients' cholesterol levels are measured again.The comparison of cholesterol levels before versus after administering the drug is an example of testing the difference between:

A) Two means from independent populations.
B) Two population variances from independent populations.
C) Two population proportions.
D) Matched pairs from two dependent populations.