Researchers examined 100 people suffering from herniated disks in their backs. Five of them were found to have a defect in a particular gene. The researchers also examined 100 people who had no problems with the disks in their backs; none had the genetic defect. They concluded that the genetic defect increases the likelihood of herniated disks. Which one of the following, if true, most strengthens the researchers' reasoning? ['Another team of researchers examined a different group of 100 people who suffered from herniated disks, and they found that none of them had the defective gene.', 'The researchers also examined a group of 100 people who did not have the defective gene; 80 were found to have herniated disks in their backs.', 'When the researchers examined the family of one of the subjects who did not suffer from herniated disks, they found 30 family members who did not have the defective gene, and 20 of them suffered from herniated disks.', 'When the researchers examined the families of the 5 subjects who had the defective gene, they found that 30 family members also had the defective gene, and each of them suffered from herniated disks.']