The role of a "leader sequence" is to A. directly control transcription. B. determine whether transcription can proceed through the genes in the operon. C. determine whether RNA polymerase can bind. D. terminate transcription. E. direct the looping of the DNA that prevents transcription initiation.

The role of a "leader sequence" is to B. determine whether transcription can proceed through the genes in the operon.

Explanation:

The "leader sequence" is the 5′ untranslated region (5′ UTR). Its main function is the regulation of translation of a transcript using different mechanisms.  They differ depending we are talking about  eukaryotes or prokaryotes (more complex). It determines whether transcription can proceed through the genes in the operon. The operon is  is a functioning unit of DNA that is made of a cluster of genes under the control of a single promoter.