A molding machine in a factory was not working very well. About a third of the time, the plastic squirt guns that it was making come out with a flaw in the handle. The repair mechanic adjusted the stamping pressure. Then she ran one gun through. It came out just fine, so she figured she had solved the problem. What was/were the error(s) in the conclusion of the repair mechanic? a. Not enough subjects
b. Subjects were not similar
c. Conditions were not kept the same
d. The experiment was not reproduced

Pick more than one, please. Much appreciated :)))