详解
Choice A is the best answer. The previous question asks what Lincoln believes is the result of breaking the laws, with the answer being that such actions undermine a nation's values. This is supported in lines 9-12("let every man...liberty"): "let every man remember that to violate the law, is to trample on the blood of his father, and to tear the character of his own, and his children's liberty."
Choices B, C, and D are incorrect because the lines cited do not support the answer to the previous question regarding what Lincoln contends happens when citizens break the law, instead explaining exactly which groups Lincoln believes should vow to follow the laws (choice B), illustrating how Lincoln believes unjust laws should be dealt with (choice C), and stating Lincoln's belief that no law is ever improved through mob rule (choice D).