Think about the argument that the motor coach driver is making. Professional drivers are competent, and they currently obey the speed limit. If the speed limit is lowered, this will force them to break the law. (They will break the new speed limit.)
The police officer disagrees, saying that all drivers, professional or otherwise, are capable of driving within the legal limit. So reducing the speed limit doesn't force anyone to break the law.
What is the point at issue? Where do these two disagree? They disagree about whether or not reducing the speed limit will cause people to break the law. The driver says it will, the police officer says it won't. This is the point at issue which is best reflected by answer choice C.
