a$13.$ Simpose that records for students $($otn$,$ name, surname$)$ have been stored in a xML fle $($students ami$).$ Which code checks if the sludent number entered by user $($to textbosi$)$ already exists in the file?

a xoociment Liat $=$ xoocument $1.$

iftestilonI. Text wnodel MestageBos. Sho $\text{'}$stn$\text{'})$

foreach $($var nade in Ust. Eiements $["$ student'$).$Elements $("$ sta"$))$

if$($textBox$1.$ Text$=$nnode Value$).$ MessageSox Show$("$Already Existst$7\text{'}?$

foreach $($var node in Lit$("$student$").$ Elements$("$stn$"))$

If$($textBov$1$ Text ranode$)$ MessageBox.Show$(\text{'}$Atready Exists$)\text{'})$;

d$.$ XElement Las $=$ XElement. Load$[\text{'}$d$///$students $mm)$:

foreach $($var node in List Elements$(\text{'}$student$")$ Elements$("$stn$"))$

If$($textbox$].$ Text anode$)$ MessageBox.Show $("$Already Existsi'?$)$