#include <bits/stdc++.h>
#define DAU  ios::sync_with_stdio(false); fin.tie(0); fout.tie(0);
#define PLEC fin.close(); fout.close(); return 0;
using namespace std;
const string problem("amenzi");
ifstream fin(problem + ".in");
ofstream fout(problem + ".out");
using PII = pair<int, int>;
using VP  = vector<PII>;
using VVP = vector<VP>;
using VI  = vector<int>;
using VVI = vector<VI>;
const int TMAX(3505);
VVI dp, a;
VVP g;
int n, m, k, p, x, y, w;
int main() {
    DAU
    fin >> n >> m >> k >> p;
    g = VVP(n + 1);
    for (int i = 1; i <= m; ++i) {
        fin >> x >> y >> w;
        g[x].emplace_back(y, w);
        g[y].emplace_back(x, w);
    }
    a = VVI(TMAX, VI(n + 1));
    for (int i = 1; i <= k; ++i) {
        fin >> x >> y >> w;
        a[y][x] += w;
    }
    dp = VVI(TMAX, VI(n + 1, -1e9));
    dp[0][1] = a[0][1];
    for (int t = 0; t < TMAX; ++t)
        for (int x = 1; x <= n; ++x) {
            if (t) dp[t][x] = max(dp[t][x], dp[t-1][x] + a[t][x]);
            if (!t || (t && dp[t][x] > dp[t-1][x]))
                for (const PII& P : g[x]) {
                    tie(y, w) = P;
                    if (t + w < TMAX)
                        dp[t+w][y] = max(dp[t+w][y], dp[t][x] + a[t+w][y]);
                }
        }
    for (int i = 1; i <= p; ++i) {
        fin >> x >> y;
        fout << max(dp[y][x], -1) << '\n';
    }
    PLEC
}