#include <climits>
#include <fstream>

#define NMAX 160
#define TMAX 3510

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

int n, m;
int rf[NMAX][NMAX];

int k;
int ev[NMAX][TMAX];

int p;
int dp[NMAX][TMAX];

inline int min(int x, int y) {
    return x < y ? x : y;
}

inline int max(int x, int y) {
    return x > y ? x : y;
}

int main() {
    int x, y, z;
    fin >> n >> m >> k >> p;

    for (int i = 1; i <= n; i++)
        for (int j = i; j <= n; j++)
            rf[i][j] = rf[j][i] = INT_MAX;

    for (int i = 0; i < m; i++) {
        fin >> x >> y >> z;
        rf[x][y] = rf[y][x] = z;
    }

    for (int i = 0; i < k; i++) {
        fin >> x >> y >> z;
        ev[x][y] = z;
    }

    for (int k = 1; k <= n; k++)
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++)
                if (i != j)
                    if (rf[i][k] != INT_MAX && rf[k][j] != INT_MAX)
                        rf[i][j] = min(rf[i][j], rf[i][k] + rf[k][j]);

    for (int i = 2; i <= n; i++)
        dp[i][0] = -1;

    for (int j = 1; j < TMAX; j++)
        for (int i = 1; i <= n; i++) {
            dp[i][j] = dp[i][j - 1];
            for (int k = 1; k <= n; k++)
                if (i != k && j >= rf[k][i])
                    dp[i][j] = max(dp[i][j], dp[k][j - rf[k][i]]);

            if (dp[i][j] != -1)
                dp[i][j] += ev[i][j];
        }

    for (int i = 0; i < p; i++) {
        fin >> x >> y;
        if (dp[x][y] == -1)
            fout << "-1\n";
        else
            fout << dp[x][y] - ev[x][y] << '\n';
    }

    fout.close();
    return 0;
}