Several studies showed that after eating a low-fat cereal for two meals a day, subjects had lost some weight. A cereal company financed this research. Identify what is wrong

a. Since the research is composed of voluntary responde samples, there many be key data points missing

b. It is not possible to take accurate measurements

c. It is questionable that the sponsor is a cereal company because this sponsor can be greatly affected by the conclusion

d. The data used In the studies is not reliable because it was not measured by the administrator.