The correct answer is D. ENIAC.
ENIAC (Electronic Numerical Integrator and Computer) was the first general-purpose electronic computer. It was built at the University of Pennsylvania’s Moore School of Electrical Engineering and was completed in 1946. ENIAC was used to calculate ballistics tables for the U.S. Army during World War II. It was also used for a variety of other scientific and engineering calculations.
UNIC (Universal Automatic Computer) was a mainframe computer developed by the U.S. Navy. It was completed in 1950 and was used for a variety of scientific and engineering calculations.
FUNTRIA (Fundamental Theory Research Institute Automatic Computer) was a mainframe computer developed by the Soviet Union. It was completed in 1956 and was used for a variety of scientific and engineering calculations.
BRAINIA (Brainiac) was a mainframe computer developed by the U.S. Air Force. It was completed in 1956 and was used for a variety of scientific and engineering calculations.
ENIAC was the first general-purpose electronic computer, and it was used for a variety of scientific and engineering calculations. UNIC, FUNTRIA, and BRAINIA were also mainframe computers, but they were developed later than ENIAC and were not as widely used.