Will mark brainliest!
What are alleles?

1. The decoders of the DNA message
2. A measurable factor
3. The basic unit of inheritance
4. Two forms of single genes

4. Two forms of single genes

Explanation:

because an allele is a variant form of a given gene Which means it is one of two or more versions of a known mutation at the same place on a chromosome.

Hope this helps

it's c (engineer's do their work with mechanical stuff not on any living being)