No not really it was sad though :\
It is a federal law that was designed to regulate the railroad industry, particularly it's monopolistic practices.
The correct answer is D, because "their" signifie that they are having "their" conversation, and that they own the conversation. C is incorrect because "there" describes where, B is incorrect because "they" describe who, and A is incorrect because "they are" doesn't grammatically or sensibly fit in, so the answer is D.