Consider the following combinational function block involving four Boolean…

Consider the following combinational function block involving four Boolean variables $x,\:y,\:a,\:b$ where $x,\:a,\:b$ are inputs and $y$ is the output.

f (x, y, a, b)
{
    if (x is 1) y = a;
    else y = b;
}

Which one of the following digital logic blocks is the most suitable for implementing this function?