Quick subprime/housing question

I am trying to wrap my pea-sized mind around the primary cause of this subprime/housing mess and would appreciate some help. As far as I'm aware, the situation not too long ago was that credit was loose, markets were flush with liquidity, housing prices were constantly on the rise. Along with the profitability of securitization and CDOs, a lot of wannabe homeowners received (or were suckered into) subprime loans.

Now, what exactly happened to make everything worse off? I can imagine a few different things:

a) Interest rates had risen due to monetary policy, and mortgages (especially adjustable rate mortgages) were finally catching up, leading to more defaults, which led to lower home prices. This cycle repeated and CDOs suddenly looked pretty ugly.

b) Home prices fell, preventing people from refinancing their mortgages, which led to defaults, lower demand for homes, and, once again, a negative feedback loop.

c) ARMs began to see greater default rates as the resets surprised many homeowners. This, of course, feeds into the aforementioned cycle/loops.

Basically, I'm not sure what triggered everything. Was it rising interest rates, which messed with ARMs? Are falling home prices the cause of all these problems (because homeowners can no longer refinance), or are falling home prices merely a symptom of something else? In my mind, the whole precarious setup rested on continuously rising home prices. Would you guys agree?