Consider the system given by the following difference equation:

y$($nT$)=$x$($nT$)+0\mathrm{.}5$y$($nT$-$T$)+0\mathrm{.}5$y$($nT$-2$T$)$

Assuming the sampling frequency of $2000$ Hz $,$ the amplitude response at f$=1000$Hz is:

$1$

$1\mathrm{.}5$

$0\mathrm{.}5$