All Cells in a Given Mammal Carry the Same Genome

All cells in a given mammal carry the same genome, yet certain genes are expressed only in a particular tissue, such as in the eye, and not expressed in other tissues, such as in the liver.How is this specificity of gene expression for a particular tissue achieved?

A) Different tissues inactivate whole swaths of the genome, like a Barr body, thereby achieving tissue-specific gene expression.
B) Different tissues express unique transcription factors that are bound to tissue-specific enhancer elements, thereby achieving tissue-specific gene expression.
C) All different cell types in the organism express all proteins equally and degrade the proteins that they don't need.
D) Certain organ and tissue systems, such as the nervous system, form relatively early in the organism's embryonic life, as compared to the epidermis; it is this relative age of the tissue lineage that determines which tissue-specific genes are expressed.
E) Each tissue has a unique RNA polymerase holoenzyme that achieves tissue-specific gene expression.