This is a question we had in an AP World History test last week:
I was able to answer (c) correctly (improvements in sea navigation and technology caused more and more people to transition from land-trading to sea-trading), but I had no idea how to answer questions (a) and (b).
I haven't been able to find this question online, and I just don't know what accounts for the pattern of the caravanserai (it seems that Persia and the Middle East has a much higher density of caravanserai, essentially the "pattern", but I don't know what to use to explain that). In the test, the answers I put were that the increase in trade and the use of caravans resulted in the increase in the number of caravanserai (doesn't really describe the "pattern" of them though).
Can somebody please point me in the right direction?