The MyoD Transcriptional Regulator Is Normally Found in Differentiating Muscle

The MyoD transcriptional regulator is normally found in differentiating muscle cells and participates in the transcription of genes that produce muscle-specific proteins, such as those needed in contractile tissue.Amazingly, expression of MyoD in fibroblasts causes these cells derived from skin connective tissue to produce proteins normally only seen in muscles.However, some other cell types do not transcribe muscle-specific genes when MyoD is expressed in them.Which of the following statements below is the best explanation of why MyoD can cause fibroblasts to express muscle-specific genes?

A) Unlike some other cell types, fibroblasts have not lost the muscle-specific genes from their genome.
B) The muscle-specific genes must be in heterochromatin in fibroblasts.
C) During their developmental history, fibroblasts have accumulated some transcriptional regulators in common with differentiating muscle cells.
D) The presence of MyoD is sufficient to activate the transcription of muscle-specific genes in all cell types.