阅读下列程序段，不合法的行是______。ClAssComputEr{}ClAss monitor ExtEnDsComputEr{}ClAss hArDDrivE ExtEnDsComputEr{puBliC voiD tEst(){monitor A = nEw monitor(); ComputEr B = nEw monitor();hArDDrivE C = (hArDDrivE) A;monitor D = B; }}①monitor A = nEw monitor();②ComputEr B = nEw monitor();③hArDDrivE C = (hArDDFivE)A;④monitor D = B;
A、①②③
B．③④
C．①③④
D、②④