IQ levels: A study investigated whether there are differences between the mean IQ level of people who were reared by their biological parents and those who were reared by someone else. What is the null hypothesis in this case? Group of answer choices a. The mean IQ level of people who were reared by their biological parents is higher than the mean of those who were not. b. The mean IQ level of people who were reared by their biological parents is lower than the mean of those who were not. c. There is no difference between the mean IQ levels of people who were reared by their natural parents and those who were not. d. There is a difference between the mean IQ levels of people who were reared by their natural parents and those who were not.