program amenzi;
  type lista=^celula;
       celula=record
                info:longint;
                timp:longint;
                next:lista;
              end;


  var n,m,k,p,i,x,y,z,j,h:longint;
      d:array [1..150] of lista;
      a,b:array [1..150,0..3500] of int64;
      r:lista;


begin
  assign(input,'amenzi.in');
  reset(input);

  assign(output,'amenzi.out');
  rewrite(output);


  readln(n,m,k,p);

  for i:=1 to m do
    begin
      readln(x,y,z);
      new(r);
      r^.info:=y;
      r^.timp:=z;
      r^.next:=d[x];
      d[x]:=r;
      new(r);
      r^.info:=x;
      r^.timp:=z;
      r^.next:=d[y];
      d[y]:=r;


    end;

  for i:=1 to n do
    begin
      new(r);
      r^.info:=i;
      r^.timp:=1;
      r^.next:=d[i];
      d[i]:=r;
    end;

  for i:=1 to k do
    begin
      readln(x,y,z);
      b[x,y]:=b[x,y]+z;
    end;

  for i:=0 to 3500 do
    for j:=1 to n do a[j,i]:=-1;
  a[1,0]:=0;
  for i:=1 to 3500 do
    begin
      for j:=1 to n do
        begin

          r:=d[j];
          while (r<>nil) do
            begin
              if i-r^.timp>=0 then
                if a[r^.info,i-r^.timp]<>-1 then
                  if  a[r^.info,i-r^.timp] >=a[j,i] then a[j,i]:= a[r^.info,i-r^.timp];
             r:=r^.next;
           end;
         { for h:=1 to n do
            begin
              if d[j,h]>0 then
                if (i-d[j,h]>=0)then
                  if (a[h,i-d[j,h]]<>-1) then
                    if a[h,i-d[j,h]]>=a[j,i] then a[j,i]:=a[h,i-d[j,h]];

            end;}

          if a[j,i]<>-1 then a[j,i]:=a[j,i]+b[j,i];
        end;
    end;
  for i:=1 to p do
    begin
      readln(x,y);
      writeln(a[x,y]);
    end;


  close(output);
end.