#include <bits/stdc++.h>
#define pb emplace_back
using i64 = long long;

const i64 INF = 1e16;
const int maxn = 2e5 + 5;
int n,Q,k,a[maxn],d[maxn],ans,f[maxn][20],lg[maxn];
std::vector<int> G[maxn];
i64 val[maxn],dp[maxn];

void dfs(int u,int fa) {
	for(auto& v : G[u]) {
		if(v == fa)continue ;
		d[v] = d[u] + 1;
		f[v][0] = u;
		for(int k = 1;(1 << k) <= d[v];++ k)
			f[v][k] = f[f[v][k - 1]][k - 1];
		val[v] = a[v] + val[u];
		dfs(v , u);
		ans = std::max(ans , d[v]);
	}
} 

int LCA(int u,int v) {
	if(d[u] < d[v])std::swap(u , v);
	for(int k = lg[d[u]];~ k;-- k) {
		if(d[u] - (1 << k) >= d[v])u = f[u][k];
		if(u == v)return u;
	}
	for(int k = lg[d[u]];~ k;-- k) {
		if(f[u][k] != f[v][k])
			u = f[u][k],v = f[v][k];
	}
	return f[u][0];
}

namespace subtask {
	int main() {
		while(Q --) {
			int u,v;
			scanf("%d %d",&u,&v);
			int t = LCA(u , v);
			printf("%lld\n",val[u] + val[v] - val[t] - val[f[t][0]]);
		}
		return 0;
	}
}

int b[maxn],cnt,c[maxn],tot;

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("%d",&a[i]);
	for(int i = 1;i < n;++ i) {
		int u,v;
		scanf("%d %d",&u,&v);
		G[u].pb(v);
		G[v].pb(u);
	}
	for(int i = 2;i <= n;++ i)
		lg[i] = lg[i >> 1] + 1;
	dfs(1 , 0);
	if(k == 1) {
		subtask::main();
		return 0;
	}
	while(Q --) {
		int u,v,t;
		cnt = tot = 0;
		scanf("%d %d",&u,&v);
		t = LCA(u , v);
		for(;u != t;u = f[u][0])b[++ cnt] = u;
		for(;v != t;v = f[v][0])c[++ tot] = v;
		b[++ cnt] = u;
		while(tot)b[++ cnt] = c[tot --];
		dp[1] = a[b[1]];
		puts("TEST:");
		for(int i = 1;i <= cnt;++ i)printf("%d ",a[b[i]]);
		puts("");
		for(int i = 2;i <= cnt;++ i) {
			dp[i] = INF;
			for(int j = i - 1;j >= i - k&&j >= 1;-- j) {
				dp[i] = std::min(dp[i] , dp[j] + a[b[i]]);
			}
		}
		printf("%lld\n",dp[cnt]);
	}
	return 0;
}