Learn English – When should I use “opportunity of” and when “opportunity from”

I'm not surprised you are getting different answers to some of these, because this is just the sort of thing that tends to vary quite a bit by region. For instance, as someone raised in California, I say that I am "in line", meaning I am waiting in line. Others (I believe this is a northeastern thing, but I may be wrong) say "on line", which has always sounded very odd to me.

One of the reasons you get this kind of variation, I'm afraid, is precisely because there are no consistent rules. Or rather, I should say, that there are many cases where one or the other could be used depending on how you conceptualize the situation, and these are just conventional. For instance, in your bus example: on the one had you are definitely inside the bus, but on the other you have boarded and stepped onto (not on top of) the bus, so you can see how the latter may have come about.

For my dialect, it's: "good luck on" and "on the list".

Though I think both variants sound fine too.

You can use "against" when there is a tangible threat:

Mace allows people to protect themselves against assault.

And you can use "from" when there is a non-tangible threat:

Not caring can protect you from feeling embarrassed.

The relevant distinction is contained in the meanings for from and against:

against — in resistance to or defense from: "protection against burglars."

from — (used to indicate agent or instrumentality): "death from starvation."

Pragmatically, there is very little difference between the two prepositions and you can more or less use them interchangeably. That being said, patterns do exist.

1. Food protects one from starvation.

2. Food protects against starvation.

Note that "one" is used in (1). You could say "protects from starvation" but it isn't as common. Likewise, you could say "protects one against starvation" but it is also more uncommon.

You can use NGrams to check the most common prepositions for each:

• protects * against
• protects * from

This can give you a quick overview of which is used where. But, as I mentioned earlier, it isn't a major issue if you use the "wrong" one. The differences here are minute.