What combination of alleles could produce a trait controlled by a recessive allele?

I don't know. But alleles is one or more alternative form of a gene, and recessive allele is two genetic genes that the offspring inherited from both parents.

So you have dominant alleles that are represented by capitals and recessive represented by lowercase, we'll just use B and b in this example. Genes are expressed from combination of 2 alleles that are either BB, Bb, or bb, when there's at least 1 dominant (capital) then the dominant trait is expressed, and only if there are 2 recessive is the recessive trait expressed.

so it would only be 2 recessive alleles.