In which of the following situations would it be appropriate to use a paired t-test to analyze the data?

Twins are screened for potential an environmental cancer risk factor and given an environmental risk factor score. Their outcomes are recorded and compared to their twin who had not been exposed to the same risk factor.

Participants are randomly assigned to a placebo or a control of a new cancer treatment to see if the medication is effective.

Patients being treated for cancer are asked whether they like their current treatment plan or not.

A researcher interviews 20 cancer patients and analyzes each interview for metaphorical themes and then summarizes the most common themes.