Which one of the following most accurately describes the author’s main ... ...

Which one of the following most accurately describes the author’s main purpose in the passage?
(A) to illustrate the ways in which a revised theoretical model can be applied to problematic cases for which previous versions of the theory offered no plausible explanation
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in PT71 (Dec 2013): Reading Comprehension