The utility company has announced that it will permanently close its Unit I nuclear power plant, the first plant that had been built by private industry and the model for a generation of modem nuclear reactors. a, that had been built by private industry and b. built by private industry and 为什么此处应选择A,(xdf说过有过去完成时必定出现过去时我就毫不犹豫的选了b)