Angry farmers in Corn county organised a series of roadblocks between Corn City and Port City to protest against new export taxes. The diagram below shows the road network between the two cities. The locations of potential roadblocks are labelled from A to D. Suppose that roadblocks are set up independently and with a known probabilityr at each checkpoint, as indicated in the diagram. (a) What is the probability of having no open road between Corn City,' and Port City? (6 MARKS) (b) What is the probability of having at least one open road given that there is a roadblock at checkpoint A? (4 MARKS) (c) Suppose that no road is open between the two cities. What is the probability that there is a roadblock at checkpoint A? {4 MARKS)