> #include<cstdio>
> #include<cstring>
> const int N=50005;
> int n,m;
> struct qq
> {
> 	int x;
> 	int y;
> 	int last;
> };
> qq s[N*2];
> qq s1[N*2];
> qq s2[N*2];
> int k[N];
> int last[N];
> int last1[N];
> int last2[N];
> int ans[N];
> int num=0,num1=0;
> int f[N];
> bool p[N];
> int up[N];
> int down[N];
> int max[N];
> int min[N];
> int Max (int x,int y){return x>y?x:y;}
> int Min (int x,int y){return x<y?x:y;}
> void init (int x,int y)
> {
> 	num++;
> 	s[num].x=x;
> 	s[num].y=y;
> 	s[num].last=last[x];
> 	last[x]=num;
> }
> void init2 (int u,int k)
> {
> 	num1++;
> 	s2[num1].x=k; 
> 	s2[num1].last=last2[u]; 
> 	last2[u]=num1;
> }
> void init1 (int x,int y,int z)
> {
> 	s1[z].x=x;
> 	s1[z].y=y;
> 	s1[z].last=last1[x];
> 	last1[x]=z;
> }
> 
> int find (int x)
> {
> 	if (f[x]==x) return f[x];
> 	int fa1=f[x];
> 	f[x]=find(f[x]);
> 	up[x]=Max(up[x],Max(up[fa1],max[fa1]-min[x]));
> 	down[x]=Max(down[x],Max(down[fa1],max[x]-min[fa1]));
> 	max[x]=Max(max[x],max[fa1]);
> 	min[x]=Min(min[x],min[fa1]);
> 	return f[x];
> }
> void TJ (int x)
> {
> 	for (int u=last1[x];u!=-1;u=s1[u].last)
> 		if (p[s1[u].y])
> 		{
> 			int lca=find(s1[u].y);
> 			init2(lca,u);
> 		}
> 	
> 	f[x]=x;
> 	p[x]=true;
> 	for (int u=last[x];u!=-1;u=s[u].last)
> 	{
> 		if (p[s[u].y]==false)
> 		{
> 			TJ(s[u].y);
> 			f[s[u].y]=x;
> 		}
> 	}
> 	for(int u=last2[x];u!=-1;u=s2[u].last)
>     {
>         int k=s2[u].x,x=s1[k].x,y=s1[k].y;
>         if (k>m)
>         {
>         	k-=m;
>         	int t1=x;x=y;y=t1;
>     	}
>         find(x); find(y);
>         ans[k] = Max(up[x] , down[y]);
>         ans[k] = Max(ans[k] , max[y] - min[x]);
>     }
> }
> int main()
> {
> 	while (scanf("%d",&n)!=EOF)
> 	{
> 	num=0;num1=0;
> 	memset(last2,-1,sizeof(last2));
> 	memset(p,false,sizeof(p));
> 	memset(last,-1,sizeof(last));
> 	memset(last1,-1,sizeof(last1));
> 	for (int u=1;u<=n;u++)
> 	{
> 		int a;
> 		scanf("%d",&a);
> 		max[u]=min[u]=a;
> 		up[u]=down[u]=0;
> 	}
> 	for (int u=1;u<n;u++)
> 	{
> 		int x,y;
> 		scanf("%d%d",&x,&y);
> 		init(x,y);
> 		init(y,x);
> 	}
> 	scanf("%d",&m);
> 	for (int u=1;u<=m;u++)
> 	{
> 		int x,y;
> 		scanf("%d%d",&x,&y);
> 		init1(x,y,u);
> 		init1(y,x,u+m);
> 	}
> 	TJ(1);
> 	for (int u=1;u<=m;u++) printf("%d\n",ans[u]);
> 	}
> 	return 0;
> }