Obě odpovědi jsou gramaticky správně, ale there's only little
left (zbývá málo) nezní idiomaticky [=
přirozeně) v hovorovém stylu a rodilý mluvčí to nejspíš neřekne –
viz Ngram.
Zbývá málo, a proto ho potřebujeme koupit
- there's not much left, so we need to buy/get some more
- there's only a little left, so we need to …
- there's only a bit left, so we need to …
- there's only a little bit left, so we need to …
- there's hardly any left, so we need to …
- there's almost none left, so we need to …
- we've almost run out [skoro nám došel], so we
need to
- we're practically out, so we need to …
I’ve gone on a big Sunday evening shop for the upcoming week only to arrive
home and realize we’re practically out of milk.
And milk was the one thing I didn’t buy because I thought we were stocked
up. (badhomecooking)
Both answers are grammatically correct, but there's only little
left doesn't sound idiomatic (natural) in conversational style and a
native speaker is unlikely to say it.