#include <bits/stdc++.h>
using namespace std;
long long n, q, k, v[200100], cnt = 0, hd[200100];
long long d[200100], f[200100];

struct edge {
	int t, n;
} e[400100];

void add(int x, int y) {
	e[++cnt].t = y;
	e[cnt].n = hd[x];
	hd[x] = cnt;
}

int dfs(int x, int fa) {
	d[x] = d[fa] + 1;
	f[x] = fa;
	for (int i = hd[x]; i; i = e[i].n) {
		int ver = e[i].t;
		if (ver == fa)
			continue;
		dfs(ver, x);
	}
	return 0;
}

int lca(int x, int y) {
	int s = x, e = y;
	long long ans = 0;
	if (d[x] != d[y]) {
		while (d[x] < d[y]) {
			ans += v[y];
			y = f[y];
		}
	}
	if (x == y)
		return ans * 2 + v[y] * 2 - v[s] - v[e];
	while (x != y) {
		ans += v[x];
		ans += v[y];
		x = f[x];
		y = f[y];
	}
	return ans * 2 + 2 * v[x] - v[s] - v[e];
}

int main() {
	freopen("csp2022_transmit.in", "r", stdin);
	freopen("csp2022_transmit.out", "w", stdout);
	cin >> n >> q >> k;
	for (int i = 1; i <= n; i++) {
		cin >> v[i];
	}
	for (int i = 1; i < n; i++) {
		int x, y;
		cin >> x >> y;
		add(x, y);
		add(y, x);
	}
	d[1] = 1;
	dfs(1, 1);
	for (int i = 1; i <= q; i++) {
		int x, y;
		cin >> x >> y;
		cout << lca(x, y) << endl;
	}
	return 0;
}