PYQ-2014-1-Mark-Logic-Gate

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?  [GATE||2014||SET3||MCQ||1MARKS]