Please explain

Lance gives the rule: "If experience teaches us nothing else, it teaches us that every general rule has at least one exception." Frank points out that Lance has just given a general rule that if assumed to be true, would mean that there is one general rule, i.e. the one that Lance gave, that has no exceptions, which would go against Lance's rule that every rule has an exception. Meaning, Lance's rule does not stand. So, Frank has pointed out that Lance's rule contradicts itself, i.e. answer choice (B): "showing that Lance's conclusion involves him in a contradiction." Hope that clears things up! Please let us know if you have any other questions.

please explain may not D. thanks

^