Which of the Following Represents a Limitation (I

Multiple Choice

Which of the following represents a limitation (i.e.,a threat to internal validity) for any correlational study of the relationship between smoking and lung cancer?

A) Some relevant factors could not be examined in a correlational study,but all these factors could be directly manipulated in an experiment.
B) A correlational study about smoking is more difficult to set up than a controlled experiment.
C) Smoking incidence could be confounded with other variables that might increase susceptibility to cancer.
D) It is not possible to construct a contingency table that maps out the relationship between variables.