#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=2e5+5;
int n,q,k,v[N],tot,cnt,id[N],head[N<<1],dfn[N],dep[N],FA[N],top[N],siz[N],b_son[N],low[N],dp[N];
struct edge{
	int ne,v;
}e[N<<1];
void add(int u,int v){
	e[++tot]={head[u],v};head[u]=tot;
}
void dfs1(int u,int fa){
	siz[u]=1;
	dep[u]=dep[fa]+1;
	FA[u]=fa;
	for(int i=head[u];i;i=e[i].ne){
		int v=e[i].v;
		if(v==fa) continue;
		dfs1(v,u);
		siz[u]+=siz[v];
		if(!b_son[u]||siz[v]>siz[b_son[u]]){
			b_son[u]=v;
		}
	}
}
void dfs2(int u,int fa,int Top){
	dfn[u]=++cnt;
	id[cnt]=u;
	top[u]=Top;
	if(b_son[u])
		dfs2(b_son[u],u,Top);
	for(int i=head[u];i;i=e[i].ne){
		int v=e[i].v;
		if(v==b_son[u]||v==fa) continue;
		dfs2(v,u,v);
	}
	low[u]=cnt;
}

struct SegTree{
	int val[N<<2],tag[N<<2],len[N<<2];
	int lc(int x) {
	return x<<1;
	}
	int rc(int x){
		return x<<1|1;
	}
	void pushup(int x){
		val[x]=val[lc(x)]+val[rc(x)];
	}
	void upd(int x,int v){
		val[x]=val[x]+len[x]*1ll*v;
		tag[x]=tag[x]+v;
	}
	void pushdown(int x){
		if(tag[x]){
			upd(lc(x),tag[x]);
			upd(rc(x),tag[x]);
			tag[x]=0;
		}	
	}
	void build(int x,int l,int r){
		len[x]=r-l+1;val[x]=tag[x]=0;
		if(l==r) {
			val[x]=v[id[l]];
			return;
		}
		int mid=(l+r)>>1;
		build(lc(x),l,mid);
		build(rc(x),mid+1,r);
		pushup(x);
	}
	int query(int x,int ql,int qr,int l,int r){
		if(ql<=l&&qr>=r) return val[x];
		pushdown(x);
		int mid=(l+r)>>1;
		int res=0;
		if(ql<=mid) res=res+query(lc(x),ql,qr,l,mid);
		if(qr>mid) res=res+query(rc(x),ql,qr,mid+1,r);
		return res;
	}
}sg;
int query(int x,int y){
	int res=0;
	while(top[x]!=top[y]){
		if(dep[top[x]]<dep[top[y]]) swap(x,y);
		res+=sg.query(1,dfn[top[x]],dfn[x],1,n);
		x=FA[top[x]];
	}
	if(dep[x]<dep[y]) swap(x,y);
	res+=sg.query(1,dfn[y],dfn[x],1,n);
	return res;
}
int query2(int x,int y){
	memset(dp,0,sizeof(dp));
	vector<int> vx,vy;
	while(top[x]!=top[y]){
		if(dep[top[x]]>dep[top[y]]){
			for(int i=dfn[x];i>=dfn[top[x]];i--) 
				vx.push_back(v[id[i]]);
			x=FA[top[x]];
		} else {
			for(int i=dfn[y];i>=dfn[top[y]];i--) 
				vy.push_back(v[id[i]]);
			y=FA[top[y]];
		}
	}
	if(dep[x]>dep[y]){
		for(int i=dfn[x];i>=dfn[y];i--) vx.push_back(v[id[i]]);
	} else {
		for(int i=dfn[y];i>=dfn[x];i--) vy.push_back(v[id[i]]);
		//for(int i=dfn[x];i<=dfn[y];i++) vx.push_back(v[id[i]]);
	}
	reverse(vy.begin(),vy.end());
	for(auto i : vy){
		vx.push_back(i);
	}
	dp[0]=vx[0];
	dp[1]=vx[0]+vx[1];
	int siz=vx.size();
	for(int i=2;i<siz;i++){
		dp[i]=min(dp[i-1],dp[i-2])+vx[i];
	}
	return dp[siz-1];
}
#undef int 
int main(){
#define int long long 
	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 a,b;
		cin>>a>>b;
		add(a,b),add(b,a);
	}
	dfs1(1,0);
	dfs2(1,0,1);
	sg.build(1,1,n);
	while(q--){
		int s,t;
		cin>>s>>t;
		if(k==1){
			cout<<query(s,t)<<'\n';
		}
		if(k==2){
			cout<<query2(s,t)<<'\n';
		}
	}
	return 0;
}