#include <cstdio>
#include <cstdlib>
#include <vector>
#include <queue>
#include <algorithm>
using namespace std;

const int NMAX = 155, TMAX = 3505;

int N, M, K, P, A, B, C, Best[NMAX][TMAX], Sum[NMAX][TMAX];
vector<pair<int, int> > G[NMAX];
bool InQueue[NMAX][TMAX];
 
 
void GetMax()
{
    for(int i = 0; i < NMAX; ++ i)
        for(int j = 0; j < TMAX; ++ j)
            Best[i][j] = -1;
            
    queue<pair<int, int> > Q;
    Q.push(make_pair(1, 0));
    Best[1][0] = Sum[1][0];
    
    while(!Q.empty())
    {
        int Node = Q.front().first, Time = Q.front().second;
        Q.pop();
        
        InQueue[Node][Time] = 0;
        for(vector<pair<int, int> > :: iterator it = G[Node].begin(); it != G[Node].end(); ++ it)
        {
            int NextTime = Time + it -> second;
            if(NextTime < TMAX && Best[Node][Time] + Sum[it -> first][NextTime] > Best[it -> first][NextTime])
            {
                Best[it -> first][NextTime] = Best[Node][Time] + Sum[it -> first][NextTime];
                if(!InQueue[it -> first][NextTime])
                    InQueue[it -> first][NextTime] = 1, Q.push(make_pair(it -> first, NextTime));
            }
        }
    }
}

int main()
{
    freopen("amenzi.in", "r", stdin);
    freopen("amenzi.out", "w", stdout);
    
    scanf("%i %i %i %i", &N, &M, &K, &P);
    for(int i = 1; i <= M; ++ i)
    {
        scanf("%i %i %i", &A, &B, &C);
        G[A].push_back(make_pair(B, C));
        G[B].push_back(make_pair(A, C));
    }
    for(int i = 1; i <= N; ++ i)
        G[i].push_back(make_pair(i, 1));
    
    for(int i = 1; i <= K; ++ i)
    {
        scanf("%i %i %i", &A, &B, &C);
        Sum[A][B] += C;
    }
    
    GetMax();
    for(int i = 1; i <= P; ++ i)
    {
        scanf("%i %i", &A, &B);
        printf("%i\n", Best[A][B]);
    }
    
    return 0;
}