If you are interested see the dictionary docs (https://docs.python.org/3/builtins/stdtypes.html#dict):

d |= other Update the dictionary d with keys and values from other, which may be either a mapping or an iterable of key/value pairs. The values of other take priority when d and other share keys. Added in version 3.9.

Pick your answer and check the Solution link.

I didn't have previous exposure to that exact syntax either, but:

• Python and plenty other languages have assignment variations with an operator like +
• | in plenty of languages means logical OR
  • possibly bitwise, but that seems unlikely in Python
• Dicts are sorta complex siblings of sets
• In terms of sets, OR is equivalent to a union

Hence, a |=b should have the same meaning as a = a | b or a = a.union(b)

and then the quiz is about basically implementation details and what the actual semantics winds up being in a language like python, where stuff is mutable by default and references are implicit (even though the zen of python states a preference for being explicit)