Both eye and liver cells contain the same genetic information. Expression patterns of 2 genes, the crystallin gene and the albumin gene, were observed in each type of cell. In liver cells, the albumin was expressed, and the crystallin gene was not. Conversely, in eye cells, the crystallin gene was expressed, and the albumin gene was not. Analysis of an upstream enhancer region for the albumin gene revealed DNA binding sites for activators A, B, and C, whereas, analysis of an upstream enhancer region for the crystallin gene revealed DNA binding sites for activators D and E. What is the best explanation for why the albumin gene is not expressed in eye cells?