Which one of the following, if true, would be the most reasonable response ... ...

Which one of the following, if true, would be the most reasonable response for the author of passage B to make to the final argument of passage A?
(A) Even under a flat-tax regime, it will be possible for some with high incomes to avoid taxes by underreporting their incomes.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in PT72 (Jun 2014): Reading Comprehension