#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[NMAX][TMAX], Sum[NMAX][TMAX], Cost[NMAX][NMAX];
vector<int> G[NMAX];
 
void GetMax()
{
    for(int i = 0; i < NMAX; ++ i)
        for(int j = 0; j < TMAX; ++ j)
            Best[i][j] = -1;
    
    Best[1][0] = 0;
    for(int j = 0; j < TMAX; ++ j)
        for(int i = 1; i <= N; ++ i)
        {
            if(Best[i][j] == -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[*it][Nextj] = max(Best[*it][Nextj], Best[i][j] + 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[A][B]);
    }
    
    return 0;
}