#include <bits/stdc++.h>

using namespace std;

const int N = 2e5 + 10;
typedef long long LL;

int n, q, k;
int hd[N], ver[N * 2], nxt[N * 2], idx, f[N][20], d[N];
LL fl[N][20], v[N];

inline void add (int x, int y) {
	ver[++idx] = y;
	nxt[idx] = hd[x];
	hd[x] = idx;
}

void bfs () {
	queue <int> q;
	q.push(1); d[1] = 1;
	while (q.size()) {
		int t = q.front(); q.pop();
		for (int i = hd[t]; i ;i = nxt[i]) {
			int y = ver[i];
			if (d[y]) continue;
			d[y] = d[t] + 1; f[y][0] = t; fl[y][0] = v[y];
			for (int j = 1;j <= log2(n);j++) {
				f[y][j] = f[f[y][j - 1]][j - 1];
				fl[y][j] = fl[y][j - 1] + fl[f[y][j - 1]][j - 1];
			}
			q.push(y);
		}
	}
}

int lca (int x, int y) {
	if (d[x] < d[y]) swap(x, y);
	for (int i = log2(n);i >= 0;i--) {
		if (d[f[x][i]] >= d[y]) x = f[x][i];
	}
	if (x == y) return x;
	for (int i = log2(n);i >= 0;i--) {
		if (f[x][i] != f[y][i]) x = f[x][i], y = f[y][i];
	}
	return f[x][0];
}

LL l (int x, int ca) {
	LL ltt = 0;
	for (int i = log2(n);i >= 0;i--) {
		if (d[f[x][i]] >= d[ca]) ltt += fl[x][i], x = f[x][i];
	}
	return ltt;
}

int main () {
	freopen("csp2022_transmit.in", "r", stdin);
	freopen("csp2022_transmit.out", "w", stdout);
	scanf("%d%d%d", &n, &q, &k);
	for (int i = 1;i <= n;i++) scanf("%lld", &v[i]);
	for (int i = 1;i < n;i++) {
		int a, b;
		scanf("%d%d", &a, &b);
		add(a, b); add(b, a);
	}
	bfs();
	while (q--) {
		int s, t;
		scanf("%d%d", &s, &t);
		int LCA = lca(s, t);
		printf("%lld\n", l(s, LCA) + l(t, LCA) + v[LCA]);
	}
	return 0;
}