Answer:
Xavier should not give the flea medication to group D.
Explanation:
In any testing of a drug normally two groups are formed.
One group is given the named as experiment group and other group is not given any medication named as controlled group.
After the completion of testing results of these two groups (experimental and controlled) are compared to find the efficacy of the drug.
Hence Xavier should not give the flea medication to group D. It should be a controlled group.