In Establishing Causality,which of the Following Conditions,in Practice,is the MOST

Multiple Choice

In establishing causality,which of the following conditions,in practice,is the MOST challenging?

A) There must exist an independent and dependent variable at the same time.
B) The two variables must be correlated.
C) The cause must precede the effect in repeated experiments.
D) The relationship between the independent variable and dependent variable must not be caused by some other factor.