#include <cstdio>
#include <cstdlib>
#include <vector>
#include <queue>
#include <algorithm>
using namespace std;
 
const int NMAX = 155, TMAX = 3505, INF = 0x3f3f3f3f;
 
int N, M, K, P, A, B, C, Best[TMAX][NMAX], Sum[NMAX][TMAX], Cost[NMAX][NMAX];
vector<int> G[NMAX];
  
void GetMax()
{
    for(int i = 0; i < TMAX; ++ i)
        for(int j = 0; j < NMAX; ++ j)
            Best[i][j] = -1;
     
    Best[0][1] = 0;
    for(int j = 0; j < TMAX; ++ j)
        for(int i = 1; i <= N; ++ i)
        {
            if(Best[j][i] == -1) continue;
            for(vector<int> :: iterator it = G[i].begin(); it != G[i].end(); ++ it)
            {
                int Nextj = j + Cost[i][*it];
                if(Nextj < TMAX)
                    Best[Nextj][*it] = max(Best[Nextj][*it], Best[j][i] + Sum[*it][Nextj]);
            }
        }
         
}
 
int main()
{
    freopen("amenzi.in", "r", stdin);
    freopen("amenzi.out", "w", stdout);
     
    scanf("%i %i %i %i", &N, &M, &K, &P);
     
    for(int i = 1; i <= N; ++ i)
        for(int j = 1; j <= N; ++ j)
            Cost[i][j] = INF;
             
    for(int i = 1; i <= M; ++ i)
    {
        scanf("%i %i %i", &A, &B, &C);
        Cost[A][B] = min(Cost[A][B], C);
        Cost[B][A] = min(Cost[B][A], C);
        G[A].push_back(B);
        G[B].push_back(A);
    }
    for(int i = 1; i <= N; ++ i)
        Cost[i][i] = min(Cost[i][i], 1), G[i].push_back(i);
     
    for(int i = 1; i <= K; ++ i)
    {
        scanf("%i %i %i", &A, &B, &C);
        Sum[A][B] += C;
    }
     
    GetMax();
    for(int i = 1; i <= P; ++ i)
    {
        scanf("%i %i", &A, &B);
        printf("%i\n", Best[B][A]);
    }
     
    return 0;
}