Thanks for the explanations all!
fujii, you've learnt something about 'rain ice' from the experience of another pilot on here, as have I. That's one of the benefits I like to get from these threads and I'm glad to see you have too!
Thanks for those who agree with me that I am actually trying to further my understanding. Oggers, the irony of the claim that I'm just trying to learn the answer is that if I've pasted a) b) c) d) then PPL Cruiser has already told me 'the answer'. But I want to understand more. I had struggled to find much on rain ice, as fujii has since, and so I came here to ask for explanations and experience. I got both and am grateful!
engineno9, I'm glad the threads provide some benefit to you. I had considered just not posting my questions here any more! You're right that something explained a different way can make something click and pprune has really helped for that.