Which of the Following Is True About Confounding Variables in Observational

Which of the following is true about confounding variables in observational studies?

A) If a confounding variable is present, then we know that a change in the explanatory variable cannot cause a change in the response variable.
B) If a confounding variable is present, it is possible that a change in the explanatory variable causes a change in the response variable, but it is hard to separate the effect of the explanatory variable and the effect of the confounding variable on the response.
C) Confounding variables are not a problem in observational studies because we only observe the explanatory and response variables.
D) Confounding variables are only a problem in observational studies if they are also interacting variables.