Answer Explanations for GMAT Prep?

there are no answer explanations from gmatprep. however, gmatclub has an index of most of those questions. you can usually do a search to look up specific questions.

to elaborate slightly on the above, if you google any sentence from a practice question, in quotes, you'll find threads from the gmat forums explaining the answers pretty clearly. same goes for any practice question from the official guide (yes, many of those have explanations in the book, but they aren't always very clear)

I concur with HerSerendipity and Dublin -- that was the approach I used to review the Official gmatprep CAT questions. I used www.beatthegmat.com (they have a search function). Just type half the CAT question in quotes and it will have been discussed and answered in detail.

Google works just fine for me. By using Google it also brings up ManhattanGMAT forum and explanations in addition to BeatTheGMAT. I find having both explanations and comparing the methodology helped me in some cases.