A Boolean function f of two variables x and y is defined as follows:
f(0, 0) = f(0, 1) = f(1, 1) = 1; f(1, 0) = 0
Assuming complements of x and y are not available, a minimum cost solution for realizing f using only 2-input NOR gates and 2-input OR gates (each having unit cost) would have a total cost of

A. 1 unit

B. 4 unit

C. 3 unit

D. 2 unit

Answer: Option D