#include <bits/stdc++.h>

using namespace std;

ifstream fin("amenzi.in");
ofstream fout("amenzi.out");

const int NMax = 150 + 5;
const int LIM = 3500;

vector < pair < int, int > > G[NMax];

int D[NMax][3505];
int A[NMax][3505];
inline void PD(const int &n) {

    memset(D, -1, sizeof(D));
    D[1][0] = 0;

    for(auto it: G[1]) D[it.first][it.second] = max(D[it.first][it.second], 0);

    for(int i = 1; i <= LIM; i++) {
        for(int j = 1; j <= n; j++) {
            D[j][i] = max(D[j][i], D[j][i - 1]);
            if(D[j][i] >= 0) D[j][i] += A[j][i];

            if(D[j][i] != -1){
                for(auto it: G[j]) {
                    if(it.second + i > LIM) continue;

                    D[it.first][it.second + i] = max(0, max(D[j][i], D[it.first][it.second + i]));
                }
            }
        }
    }
}

int main() {

    ios::sync_with_stdio();
    fin.tie(NULL);

    int n, m, k, p;
    fin >> n >> m >> k >> p;

    for(int i = 1; i <= m; i++) {
        int a, b, c;
        fin >> a >> b >> c;

        G[a].push_back({b, c});
        G[b].push_back({a, c});
    }

    for(int i = 1; i <= k; i++) {
        int a, b, c;
        fin >> a >> b >> c;

        A[a][b] += c;
    }

    PD(n);

    for(int i = 0; i < p; i++) {
        int a, b;
        fin >> a >> b;

        fout << D[a][b] << "\n";
    }

    return 0;
}