In transcription: select one:
a. several amino acids are assembled by the messenger rna molecules at one time.
b. a special sequence called a promoter is necessary for transcription to begin.
c. certain polypeptide sequences are governed by one ribosome, while other sequences are produced by other ribosomes.
d. the transfer rna molecules arrange the messenger rna codons into the appropriate sequence.
e. none of these.

Option (b).

Explanation:

Transcription is the process of formation of RNA molecule from the DNA with the help of enzymes and proteins. The transcription always occur in the 5' to 3' direction.

Transcription involves three steps- initiation, elongation and termination. The initiation of the transcription requires the special nucleotide sequence known as promoter. This sequence are the conserved sequences and RNA polymerase binds at this site.

Thus, the correct answer is option (b).