"They buy pasta? Which?"
Translation:Ils achètent des pâtes ? Lesquelles ?
Using inversion here changes the sense of the original "question" which is posed almost rhetorically. Like something you might say after someone has told you that they buy pasta. A questioning response of surprise.
Your inversion alters the meaning to a fully fledged question - "do they buy pasta?" / "are they buying pasta?".
I feel the nuance is different.
Quel / Quels / Quelle and Quelles are interrogative adjectives which have the following characteristics:
- Used in place of an article not with one
- Placed directly in front of a noun
- Must agree with the noun in gender and number
- Are identical to French exclamative adjectives (eg Quel dommage !)
and, the one that relates to your question
- Quel + noun = lequel (an interrogative pronoun).
Or, in this instance, quelles + pâtes (noun) = lesquelles.