The main characteristic of the fourth generation computer is:

A. Transistor
B. Vacuum tubes
C. Integrated circuit
D. VLSI (Very Large Scale Integrated)
E. Memory

D. VLSI (Very Large Scale Integrated)

Explanation: Fourth generation computers are characterized by the use of VLSI (Very Large Scale Integration) technology, which allowed for the integration of millions of transistors on a single chip, significantly increasing computational power. Therefore, D is the correct answer.