13. While it is often technically possible to install a single generator of sufficient capacity to satisfy all requirements, multiple generators are normally installed. One reason for multiple units is that a single generator failure would otherwise incapacitate the entire electric plant; and other is that part-load operation of a single generator would be at an excessively low power level. In what follows, which is not the reason to install the multiple generators?(A) The sufficient power capacity could not be satisfied by a single generator.(B) A single generator can not provide reliable electrical power supply when a single generator failure occurs.(C) The part-load operation of a single generator at an excessively low power level is unlikely to occur.(D) The multiple generators could also provide electrical power supply even if a single generator failure occurs.