Figure $14\mathrm{.}21$ A Bayesian network describing some features of a car's electrical system and engine. Each variable is Boolean, and the true value indicates that the corresponding aspect of the vehicle is in working order.

a$)$ Extend the network with the boolean variables IcyWeather and StarterMotor

b$)$ Give reasonable conditional probabilities for each node

c$)$ Divide the network into the canonical cases: causal networks, common cause, and common effect.