#include <bits/stdc++.h>
using namespace std;

int n, m, k, p;
int d[155][3505];
int am[155][3505];
queue <pair <int, int> > q;
vector <pair <int, int> > v[155];

inline void wutm8(){
    for(int i = 1; i <= n ; ++i)
        for(int j = 0; j <= 3500 ; ++j) d[i][j] = -2000000000;

    d[1][0] = am[1][0];
    q.push({1, 0});
    for(int i = 1; i <= 3500 ; ++i){
        d[1][i] = d[1][i - 1];
        if(d[1][i] < d[1][i - 1] + am[1][i]){
            d[1][i] = d[1][i - 1] + am[1][i];
            q.push({1, i});
        }
    }

    while(!q.empty()){
        int nod = q.front().first, timp = q.front().second;
        q.pop();
        for(auto it : v[nod]){
            if(timp + it.second > 3500) continue ;
            if(d[it.first][timp + it.second] < d[nod][timp] + am[it.first][timp + it.second]){
                q.push({it.first, timp + it.second});
                d[it.first][timp + it.second] = d[nod][timp] + am[it.first][timp + it.second];

                for(int i = timp + it.second + 1; i <= 3500 ; ++i){
                    d[it.first][i] = max(d[it.first][i - 1], d[it.first][i]);
                    if(d[it.first][i] < d[it.first][i - 1] + am[it.first][i]){
                        d[it.first][i] = d[it.first][i - 1] + am[it.first][i];
                        q.push({it.first, i});
                    }
                }
            }
        }
    }
}
int main()
{
    freopen("amenzi.in", "r", stdin);
    freopen("amenzi.out", "w", stdout);

    scanf("%d%d%d%d", &n, &m, &k, &p);
    int x, y, c;
    for(int i = 1; i <= m ; ++i){
        scanf("%d%d%d", &x, &y, &c);
        v[x].push_back({y, c});
        v[y].push_back({x, c});
    }
    for(int i = 1; i <= k ; ++i){
        scanf("%d%d%d", &x, &y, &c);
        am[x][y] += c;
    }

    wutm8();

    for(int i = 1; i <= n ; ++i)
        for(int j = 1; j <= 3500 ; ++j)
            d[i][j] = max(d[i][j], d[i][j - 1]);
    for(int i = 1; i <= p ; ++i){
        scanf("%d%d", &x, &y);
        printf("%d\n", max(d[x][y], -1));
    }

    return 0;
}