Meaning of the statement:
“Learning is often conflated with mere grammar instruction.”
Here, conflated with means wrongly treated as the same thing or mixed together.
So, the statement means that people sometimes mistakenly think that learning a language is simply the same as learning grammar rules.
Why the other options are wrong
Language learning happens through grammar instruction. ❌
This is too broad and does not express the idea of conflated.
People wrongly treat language learning and grammar instruction as the same. ✅
This exactly conveys the meaning.
Grammar instruction is unimportant. ❌
The sentence does not say grammar is unimportant.