Correct Option: D

The period of first generation computers (19461958) is referred to as the Vacuum Tube Years. The first generation computers were huge, slow, expensive, and often undependable. In 1946 Presper Eckert and John Mauchly built the ENIAC electronic computer which used vacuum tubes instead of the mechanical switches of the Mark I. The ENIAC led to other vacuum tube type computers like the EDVAC (Electronic Discrete Variable Automatic Computer) and the UNIVAC I (UNIVersal Automatic Computer).