Hmm. This question threw me off because it's asking to support the "historians' contention concerning decline in wheat PRODUCTION." It's not asking to support why there's more barley than wheat and that's also not what the historians contended. The correct answer, B, seems like it's supporting the latter.

I chose B initially but ruled it out on blind review and went with E instead because E would better justify why there's a decline in wheat production. The people ate more barley so they stopped producing wheat.

I feel like B only explains why there's more barley than wheat but it doesn't help to explain why wheat production declined. So what if barley has greater resistance to salt than wheat? How does that explain why wheat production declined?

Okay, it works now. Thank you!

Not sure if this is happening to me only or if it's temporary but all of my answers that I've inputted for each preptest have been wiped out. :/

I think you should move on to the next lessons. You can always practice identifying the conclusion in other arguments throughout the course and maybe when you come back to main point questions you'll notice improvements. You'll get a chance to learn how to identify conclusions for other question types also.

I study at the library and I found that most libraries have a small section for lsat prep books. You could use the questions in there to practice or photocopy/take a pic of the pages. And of course, make sure to go with the companies that use real lsat questions. Another option is to purchase the lsat preptest books.