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

using i64 = int64_t;

#define rep(i, x, y) for (i64 i = i64(x), i##_max_for_repmacro = i64(y); i < i##_max_for_repmacro; ++i)
#define debug(x) #x << "=" << (x)

#ifdef DEBUG
#define _GLIBCXX_DEBUG
#define print(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define print(x)
#endif

template <i64 p>
class fp {
public:
    i64 x;
    fp() : x(0) {}
    fp(i64 x_) : x((x_ % p + p) % p) {}
    fp operator+() const { return fp(x); }
    fp operator-() const { return fp(-x); }
    fp& operator+=(const fp& y) {
        x += y.x;
        if (x >= p) x -= p;
        return *this;
    }
    fp& operator-=(const fp& y) { return *this += -y; }
    fp& operator*=(const fp& y) {
        x = x * y.x % p;
        return *this;
    }
    fp& operator/=(const fp& y) { return *this *= fp(inverse(y.x)); }
    fp operator+(const fp& y) const { return fp(x) += y; }
    fp operator-(const fp& y) const { return fp(x) -= y; }
    fp operator*(const fp& y) const { return fp(x) *= y; }
    fp operator/(const fp& y) const { return fp(x) /= y; }
    bool operator==(const fp& y) const { return x == y.x; }
    bool operator!=(const fp& y) const { return !(*this == y); }
    i64 extgcd(i64 a, i64 b, i64& x, i64& y) {
        i64 d = a;
        if (b != 0) {
            d = extgcd(b, a % b, y, x);
            y -= (a / b) * x;
        } else {
            x = 1;
            y = 0;
        }
        return d;
    }
    i64 inverse(i64 a) {
        i64 x, y;
        extgcd(a, p, x, y);
        return (x % p + p) % p;
    }
};

template <i64 p>
i64 abs(const fp<p>& x) { return x.x; }

template <i64 p>
istream& operator>>(istream& is, fp<p>& x) {
    is >> x.x;
    return is;
}

template <i64 p>
ostream& operator<<(ostream& os, const fp<p>& x) {
    os << x.x;
    return os;
}

template <typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << ", " << p.second << ")";
    return os;
}

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& vec) {
    os << "[";
    for (const auto& v : vec) {
        os << v << ",";
    }
    os << "]";
    return os;
}

template <typename T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template <typename T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <typename A, typename T, size_t size>
void fill(A (&ary)[size], const T& val) {
    fill((T*)ary, (T*)(ary + size), val);
}

constexpr int inf = 1.01e9;
constexpr i64 inf64 = 4.01e18;
constexpr long double eps = 1e-9;

// double(64bit浮動小数)のn分探索のループ回数の上限(2分探索なら50でも十分かもしれない). long double(80ビットの x87 浮動小数点型?)だと, 2分探索であってもこれだと足りないケースがある気がするので, もうちょっと余裕を持たせた方が良さそう.
constexpr i64 max_loop = 100;

class union_find {
private:
    vector<int> parent, rank, gs;
    int size;

public:
    int count_group;
    union_find() = default;
    union_find(int n) { init(n); }

    void init(int n) {
        size = n;
        count_group = n;
        parent.resize(size);
        rank.assign(size, 0);
        gs.assign(size, 1);
        for (int i = 0; i < size; ++i) parent[i] = i;
    }

    int find(int x) {
        if (parent[x] == x)
            return x;
        else
            return parent[x] = find(parent[x]);
    }

    void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y) return;
        if (rank[x] < rank[y]) {
            parent[x] = y;
            gs[y] += gs[x];
        } else {
            parent[y] = x;
            gs[x] += gs[y];
            if (rank[x] == rank[y]) ++rank[x];
        }
        --count_group;
    }

    bool is_same_group(int x, int y) {
        return find(x) == find(y);
    }

    int group_size(int x) {
        return gs[find(x)];
    };
};

struct edge{
    i64 to,dist;
};


template<typename initialize, typename operate,typename predicate>
vector<i64> parallel_max_binary_search(const initialize& init, i64 num_of_operation, const operate& op, vector<i64> ok, vector<i64> ng, const predicate& p){
    while(true){
        bool finish=true;
        vector<vector<i64>> md_idx(num_of_operation);

        rep(i,0,ok.size()){
            if(ng[i]-ok[i]>1){
                finish=false;
                i64 md=(ng[i]+ok[i])/2;
                md_idx[md].emplace_back(i);
            }
        }

        if(finish) break;

        init();
        rep(i,0,num_of_operation){
            op(i);
            for(i64 idx:md_idx[i]){
                if(p(idx)) ok[idx]=i;
                else ng[idx]=i;
            }
        }
    }

    return ok;
}

void solve() {
    //constexpr i64 mod = 1'000'000'007;
    i64 N,M,K,Q;
    cin >> N >> M >> K >> Q;

    vector<i64> A(M),B(M),L(M);
    rep(i,0,M){
        cin >> A[i] >> B[i] >> L[i];
        --A[i];
        --B[i];
    }

    vector<i64> F(K);
    rep(i,0,K){
        cin >> F[i];
        --F[i];
    }

    vector<i64> S(Q),T(Q);
    rep(i,0,Q){
        cin >> S[i] >> T[i];
        --S[i];
        --T[i];
    }

    auto calc_shortest_path=[&](){
        vector<vector<edge>> graph(N+1);
        rep(i,0,M){
            graph[A[i]].emplace_back(edge{B[i],L[i]});
            graph[B[i]].emplace_back(edge{A[i],L[i]});
        }

        vector<bool> fes(N);
        rep(i,0,K) fes[F[i]]=true;

        rep(i,0,N) if(fes[i]) graph[N].emplace_back(edge{i,0});

        using pii=pair<i64,i64>;

        vector<i64> dist(N+1,inf64);
        priority_queue<pii,vector<pii>,greater<pii>> que;
        dist[N]=0;
        que.push(make_pair(0,N));

        while(!que.empty()){
            i64 u,d;
            tie(d,u)=que.top();
            que.pop();

            if(d>dist[u]) continue;

            for(auto& e:graph[u]){
                i64 v=e.to,nd=d+e.dist;
                if(nd>=dist[v]) continue;
                dist[v]=nd;
                que.push(make_pair(nd,v));
            }
        }

        dist.pop_back();
        return dist;
    };

    auto dist=calc_shortest_path();

    using tup=tuple<i64,i64,i64>;
    vector<tup> edges(M);
    rep(i,0,M){
        edges[i]=make_tuple(min(dist[A[i]],dist[B[i]]),A[i],B[i]);
    }
    sort(rbegin(edges),rend(edges));

    vector<tup> tree_edges;
    {
        union_find uf(N);
        rep(i,0,M){
            auto& e=edges[i];
            i64 d,u,v;
            tie(d,u,v)=e;
            if(uf.is_same_group(u,v)) continue;
            uf.unite(u,v);
            tree_edges.emplace_back(make_tuple(u,v,d));
        }
    }

    union_find uf(N);

    auto init=[&]{uf.init(N); };

    i64 num_of_operation=N-1;
    auto op=[&](i64 i){ uf.unite(get<0>(tree_edges[i]), get<1>(tree_edges[i])); };

    vector<i64> ok(Q,-1),ng(Q,N-1);
    auto p=[&](i64 i){ return !uf.is_same_group(S[i], T[i]); };

    auto idx = parallel_max_binary_search(init, num_of_operation, op, ok, ng, p);

    rep(i,0,Q) cout << get<2>(tree_edges[idx[i]+1]) << endl;
}

int main() {
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
    cout.setf(ios::fixed);
    cout.precision(16);
    solve();
    return 0;
}



Measured memory_bytes: 25308