Combinatorial control refers to a regulatory mechanism in which: each alternatively spliced transcript has a different combination of exons. none of the answer options is correct. transcription is terminated by a combination of sites in the terminator. transcription is initiated by a combination of sites in the promoter. transcription requires a specific combination of transcription factors.

transcription requires a specific combination of transcription factors

Explanation:

Combinatorial control refers to a regulatory mechanism in eukaryotic transcription that involves several transcriptional factors. Simply saying, in eukaryotes, expression of a gene is controlled by specific combinations of transcriptional factors. This also means that one factor can be involved in regulation of two distinct genes but in combination with different other factors.

Combinatorial control is one of the examples which shows the complexity of gene regulation in eukaryotes over the prokaryotes.

1. dermis

2. chemical

3. urine

4. viruses

5. antibodies

b. lithosphere, asthenosphere, mesosphere   is the answer most likely