41. A typical eukaryotic cell may contain tens of thousands of genes, but only a small fraction of them are expressed at the same time. In this case, (A) the default state of most genes is usually set to be on. (B) the default state of most genes is usually set to be off. (C) most un-expressed genes are deleted from the genome. (D) most expressed genes are copied several times. (E) most expressed genes are joined together.