Answer:
The correct answer is A) operator sequences
Explanation:
An operator sequence is a sequence that regulates the transcription of genes present in an operon. These operons are mainly found in prokaryotes. An operon consists of closely bound structural gene which have its own operator, and promotor and these genes are transcribed together.
An operator sequence overlaps the promoter sequence. Regulatory proteins binds to these operator sequence and prevents the binding of RNA polymerase on the promoter thereby inhibits the transcription initiation of operon in prokaryotes.
So as operator sequence is mainly found in prokaryotes so they are not hallmarks used to identify genes in an unknown eukaryotic sequence.