#include <iostream>
#include <vector>
#include <stdio.h>

using namespace std;

int n, m, k, p;

vector<int> fii[151];
vector<int> tmp[151];
vector<int> intl[2];

int pos[151][4501];
int amm[151][4501];
int ame[151][3501];

int main()
{
	int a,b,c;
	int i;
	int nodc,tmpc,j;

	freopen("amenzi.in","r",stdin);
	freopen("amenzi.out","w",stdout);

	scanf("%d %d %d %d\n", &n, &m, &k, &p);

	for ( i = 1; i <= m; ++i )
	{
		scanf("%d %d %d\n", &a, &b, &c);
		fii[a].push_back(b);
		fii[b].push_back(a);

		tmp[a].push_back(c);
		tmp[b].push_back(c);
	}

	for ( i = 1; i <= k; ++i )
	{
		scanf("%d %d %d\n", &a, &b, &c);
		if ( ame[a][b] < c ) ame[a][b] = c;
	}

	pos[1][0] = 1;

	for ( tmpc = 0; tmpc <= 3500; ++tmpc )
		for ( nodc = 1; nodc <= n; ++nodc )
	{
		if ( pos[ nodc ][ tmpc ] )
		{
			amm[ nodc ][ tmpc ] += ame[ nodc ][ tmpc ];
			for ( j = 0; j < fii[ nodc ].size(); ++j )
			{
				pos[ fii[nodc][j] ][ tmpc + tmp[nodc][j] ] = 1;
				amm[ fii[nodc][j] ][ tmpc + tmp[nodc][j] ] = max( amm[ fii[nodc][j] ][ tmpc + tmp[nodc][j] ], amm[ nodc ][ tmpc ] );
			}
			pos[ nodc ][ tmpc+1 ] = 1;
			amm[ nodc ][ tmpc+1]  = max( amm[ nodc ][ tmpc ], amm[ nodc ][ tmpc+1 ] );

		}
	}

	for ( i = 1; i <= p; ++i )
	{
		scanf("%d %d\n", &a, &b);
		if ( pos[ a ][ b ] == 0 )
			printf("-1\n");
		else	printf("%d\n", amm[ a ][ b ] );
	}

	fclose(stdin);
	fclose(stdout);

	return 0;
	
}