Answer:
Option d.
Step-by-step explanation:
Thinking process:
There two things in the question:
1. experimental set up
2. observation (a) the results, and (b) the behavior of the old people who own pets.
There is data on the experimental set up. It means that correlations cane be done to determine the significance of the results.
On the other side, the results will present more or less the common trends in the adult population who own pets. In this case, the data is representative of the total population.