#include <fstream>
#include <iostream>
#include <vector>
using namespace std;

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

const int N = 155, T = 3505, oo = (1 << 31) - 1;

int n, m, k, p, d[N][T], a[N][T];
vector <pair <int, int> > g[N];

int main() {
    fin >> n >> m >> k >> p;
    while (m--) {
        int x, y, z;
        fin >> x >> y >> z;
        g[x].push_back (make_pair (y, z));
        g[y].push_back (make_pair (x, z));
    }
    while (k--) {
        int x, y, z;
        fin >> x >> y >> z;
        a[x][y] += z;
    }
    for (int i = 1; i <= n; ++i)
        for (int j = 0; j <= T; ++j)
            d[i][j] = -oo;
    d[1][0] = 0;
    for (int j = 1; j <= T; ++j)
        for (int i = 1; i <= n; ++i) {
            d[i][j] = d[i][j-1];
            for (vector <pair <int, int> > :: iterator it = g[i].begin(); it != g[i].end(); ++it)
                if (j - (*it).second >= 0)
                    d[i][j] = max (d[i][j], d[(*it).first][j - (*it).second] + a[i][j]);
        }
    while (p--) {
        int x, y;
        fin >> x >> y;
        fout << ((d[x][y] != -oo) ? d[x][y] : -1) << "\n";
    }
}