If a Researcher Hypothesizes That Employment Causes People to Live

Multiple Choice

If a researcher hypothesizes that employment causes people to live longer,he or she may interpret an observed association between employment and number of years lived as evidence that supports his or her hypothesis.However,if adding healthiness to the model eliminates all of the original association between employment and number of years lived,this suggests that healthiness might predict both employment and longer life.This demonstrates that

A) reciprocal causality must always be considered for original hypotheses.
B) dependent variables must often be lagged for proper interpretation.
C) confounding factors present alternative explanations to original hypotheses.
D) adding new variables can change the results regarding the null hypothesis.