For #19, I can see that this experiment is randomized and controlled, but how do I know if it is double-blinded?

I answered yes for this question because I thought there could be a confounder since I don't know if this is the ideal experiment.

The following situation pertains to questions 16-20. A study was done to see whether regular exercise can help lower cholesterol. The subjects were 1000 adults with high cholesterol. Half the subjects were randomly assigned to treatment and half were randomly to control. In the treatment group, the subjects were offered the usual health care plus given full access to a gym and a personal trainer and encouraged to exercise on a treadmill for 30 minutes 4 times a week. The control group was offered just the usual health care (which had no gym access). All the subjects were followed for 1 years and their cholesterol levels were compared. 16. Is this an observational study or a designed experiment'@3esigned Experiment b) Observational Study 17. What type of controls were used? a)? . domized b) NonRandomized c) There were no controls. 18. Was there a placebo? a) Yes @ No 19. Will confounders be present in this type of study? a) Yes No