Problem Link : http://www.lightoj.com/volume_showproblem.php?problem=1110

/*
         +-+ +-+ +-+
         |R| |.| |S|
         +-+ +-+ +-+
 */

#include <bits/stdc++.h>

#define pii             pair <int,int>
#define sc              scanf
#define pf              printf
#define Pi              2*acos(0.0)
#define ms(a,b)         memset(a, b, sizeof(a))
#define pb(a)           push_back(a)
#define MP              make_pair
#define db              double
#define ll              long long
#define EPS             10E-10
#define ff              first
#define ss              second
#define sqr(x)          (x)*(x)
#define D(x)            cout<<#x " = "<<(x)<<endl
#define VI              vector <int>
#define DBG             pf("Hi\n")
#define MOD             100007
#define MAX             10000
#define CIN             ios_base::sync_with_stdio(0); cin.tie(0)
#define SZ(a)           (int)a.size()
#define sf(a)           scanf("%d",&a)
#define sff(a,b)        scanf("%d%d",&a,&b)
#define sfff(a,b,c)     scanf("%d%d%d",&a,&b,&c)
#define loop(i,n)       for(int i=0;i<n;i++)
#define REP(i,a,b)      for(int i=a;i<b;i++)
#define TEST_CASE(t)    for(int z=1;z<=t;z++)
#define PRINT_CASE      printf("Case %d: ",z)
#define all(a)          a.begin(),a.end()
#define intlim          2147483648
#define inf             1000000
#define ull             unsigned long long

using namespace std;


/*----------------------Graph Moves----------------*/
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*------------------------------------------------*/

/*-----------------------Bitmask------------------*/
int Set(int N,int pos){return N=N | (1<<pos);}
int reset(int N,int pos){return N= N & ~(1<<pos);}
bool check(int N,int pos){return (bool)(N & (1<<pos));}
/*------------------------------------------------*/

char s1[105],s2[105];
int dp[105][105];
string ans[105][105];
int n,m;

void LCS()
{
    loop(i,n+2)
    {
        dp[i][0]=0;
        ans[i][0]="";
    }
    loop(i,m+2)
    {
        dp[0][i]=0;
        ans[0][i]="";
    }

    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
    {
        if(s1[i-1]==s2[j-1])
        {
            dp[i][j]=dp[i-1][j-1]+1;
            ans[i][j]=ans[i-1][j-1]+s1[i-1];
        }
        else if(dp[i-1][j]>dp[i][j-1])
        {
            dp[i][j]=dp[i-1][j];
            ans[i][j]=ans[i-1][j];
        }
        else if(dp[i][j-1]>dp[i-1][j])
        {
            dp[i][j]=dp[i][j-1];
            ans[i][j]=ans[i][j-1];
        }
        else
        {
            dp[i][j]=dp[i-1][j];
            ans[i][j]=min(ans[i-1][j],ans[i][j-1]);
        }
    }
}

int main()
{
    ///freopen("in.txt","r",stdin);
    ///freopen("out.txt","w",stdout);
    int t;
    sf(t);
    TEST_CASE(t)
    {
        getchar();
        sc("%s %s",s1,s2);
        n=strlen(s1);
        m=strlen(s2);
        LCS();
        PRINT_CASE;
        if(dp[n][m]==0)
            pf(":(\n");
        else
            cout<<ans[n][m]<<endl;
    }
    return 0;
}