Her brain froze. So? Such? The rule: such + (adjective) + noun . So + adjective . The word “difficult” described “test” (a noun). “Such a difficult test.”

Do not confuse "a steep learning curve" with:

The phrase is a singular countable noun. So before it, you need:

But what does this phrase actually mean in the context of the Reading and Use of English paper? And more importantly, how do you find the correct when this tricky collocation appears?