Answer:
The correct answer is option e. "using a control group".
Step-by-step explanation:
Using a control group is one of the basis of any scientific research. It is essential to prove if the response that the researcher is getting is due to the factor being studied and not something else that could be present in the samples. All the investigations should use at least one control group, and using it is not a factor that may lead to different conclusions from two different studies investigating the same thing.