Answer
The function $f$ is more sensitive to a change in $d$.
Work Step by Step
$f (a,b,c,d)=ad-b c$
and
$f_a=d \\ f_b=-c \\ f_c=-b \\ f_d=a$
$\implies df = d \ da -c \ db -b \ dc +a \ d \ d$
$\implies df=2 dx +1 dy$
So, we can see that as |a| is bigger than b, c and d, the function $f$ is more sensitive to a change in $d$.
