I have always found (D) to be absolutely true.
10 year old me found (C) to be true. From the existence of thief skills we inferred that if the rules didn't provide for a chance, you weren't able to do that. I now know that was not the intention, but the rules did not expressly call out that you could attempt things not on your character sheet, and I don't think we were alone in playing that way. The problem was alleviated when non-weapon proficiencies were introduced, but by then I made the switch to multiclass characters and never had the issue again (and we dumped demihuman level limits, which I don't think was uncommon).
In my experience (B) was also true, even at first level. More non-combat encounters did not make for less combat encounters in a day, it just made for more total encounters for a day. Given how early published adventures were written (dungeon focussed, with nowhere really safe to hole up in the dungeon, often based on tournament dungeons with time pressure), I am inclined to think this was the norm.
(A) was not true RAW. However, IME a lot of groups never understood the reasoning behind granting XPs for treasure, so it often got houseruled in (I know at least one DM I played with regularly did this). And to 10 year old murder-hobos, combat was the default way of getting the treasure, so (A) might as well have been true.