Answer
The function $f$ is more sensitive to a change in $d$.
Work Step by Step
$f (a,b,c,d)=ad-b c$
So, $f_a=d; f_b=-c; f_c=-b ; f_d=a$
Next, $df = d \times da -c db -b dc +a \times dd$
We can notice that the function $f$ is more sensitive to a change in $d$ as $|a| is bigger than b, c and d.
