On question 10-6, there was some confusion on my group about what exactly is being implied by the question stem and all the italics. Is this asking for the predictor that sits most directly on the pathway of causation, or is it hinting at the presence of confounding and the possible need for instrumental variables?
You can assume that the possibility of confounding is a threat to valid causal inference (as it usually is) and that you want to minimize that threat.
Tom