When was the first CPU introduced (first Microprocessor the Intel 4004)

A (a) 1981
B (b) 1971
C (c) 1981
D (d) 1991

Why? Explanation: The Intel 4004 was a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. It was the first complete CPU on one chip, and also the first commercially available microprocessor. Such a feat of integration was made possible by the use of then-new silicon gate technology allowing a higher number of transistors and a faster speed than was possible before.