The south beach diet was given to a volunteer group of 25 people who were at least 50 pounds overweight. 18 people from the group lost at least 20 pounds. what should we conclude about the effectiveness of the diet?

nothing, since the group knew they were using the diet.
the diet is effective in 72% of people.
nothing, since the 25 people were not an srs.
nothing, since there was no control group.
people overweight by at least 50 pounds will lose more than 20 pounds on the diet.