A few questions back there was a phrase with "chìa khoá" without "chiếc" nor "cái" in the correction. Now, why is it wrong to omit "chiếc" here ?
You can technically omit it.
Same question. Why is một chìa khóa not accepted? This construction is used in other sentences.
There are lots of acceptable alternatives that aren't listed in the answers.
For me, a few questions back, "key" was "cái chìa" without the "khoá". Why would that be??
Takes 'cái chìa khoá' as well as chiếc