#include<bits/stdc++.h>
using namespace std;
int main(){
int t;cin>>t;
while(t--){
string s;cin>>s;
string ans="";int max_size=0,start=0,end=0;//ababbacabbbb
int k;cin>>k;//1
int i=0;
for(int j=1;j<s.size();j++){
int a=s[j]-'a';
int b=s[j-1]-'a';
if(abs(a-b)<=k){
if(max_size<j-i+1){
max_size=j-i+1;
start=i;end=j;
}
}else{
i=j;
}
}
for(int j=start;j<=end;j++){
ans+=s[j];
}
cout<<ans<<endl<<endl<<endl;
}
return 0;
}
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