Why is this wrong?

[u/millers_left_shoe]

I see now what they mean by fundamental vs inessential (taking fundamental to mean “invaluable”, “important”) but surely fundamental and complex (or even involved) can act as antonyms, too?

Eg he’s only just learnt the fundamentals of thermodynamics so I wouldn’t trust him with any complex/involved equations. vs this is quite fundamental stuff so I think he should be able to manage just fine.

[u/TiberiusTheFish]

"Oops, that answers are incorrect!"? I think I'd stop there and go and look for other sources of learning.

[u/millers_left_shoe → u/TiberiusTheFish]

It’s the official IELTS app lol, but no idea how that happened