只WA了第一个点，求大佬调

#include<bits/stdc++.h>
using namespace std;
int pro[600006],head[600006],nex[600006],cnt=0;
void ll(int x,int y){
	pro[++cnt]=y;
	nex[cnt]=head[x];
	head[x]=cnt;
}
int lg[600006];
int f[600006];
int cha[600006][30];
struct node{
	int x,y,z;
}a[600006];
int dianquan[600006];
int deep[600005];
bool cmp(node x,node y){
	return x.z<y.z;
}
int find(int x){
	return f[x]==x?x:f[x]=find(f[x]);
}
void merge(int x,int y){
	f[x]=y;
}
void dfs(int x,int fa){
	deep[x]=deep[fa]+1;
	cha[x][0]=fa;
	for(int i=head[x];i!=-1;i=nex[i]){
		if(pro[i]==fa){
			continue;
		}
		dfs(pro[i],x);
	}
}
int lca(int x,int y){
	if(deep[x]<deep[y]){
		swap(x,y);
	}
	while(deep[x]>deep[y]){
		x=cha[x][lg[deep[x]-deep[y]]];
	}
	if(x==y){
		return x;
	}
	for(int i=20;i>=0;i--){
		if(cha[x][i]!=cha[y][i]){
			x=cha[x][i];
			y=cha[y][i];
		}
	}
	return cha[x][0];
}
int main(){
	memset(head,-1,sizeof(head));
	int n,m;
	scanf("%d %d",&n,&m);
	for(int i=1;i<=m;i++){
		int x,y,z;
		scanf("%d %d %d",&x,&y,&z);
		a[i].x=x;
		a[i].y=y;
		a[i].z=z;
	}
	for(int i=1;i<=n+m;i++){
		f[i]=i;
	}
	sort(a+1,a+1+m,cmp);
	int now=n;
	for(int i=1;i<=m;i++){
		int x=a[i].x;
		int y=a[i].y;
		int z=a[i].z;
		int fx=find(x);
		int fy=find(y);
		if(fx==fy){
			continue;
		}
		now++;
		merge(fx,now);
		merge(fy,now);
		dianquan[now-n]=z;
		ll(now,fx);
		ll(now,fy);
	}
	for(int i=2;i<=now;i++){
		lg[i]=lg[i/2]+1;
	}
	dfs(now,0);
	for(int j=1;j<=20;j++){
		for(int i=1;i<=now;i++){
			cha[i][j]=cha[cha[i][j-1]][j-1];
		}
	}
	int q;
	scanf("%d",&q);
	while(q--){
		int x,y;
		scanf("%d %d",&x,&y);
		int fx=find(x);
		int fy=find(y);
		if(fx!=fy){
			printf("impossible\n");
			continue;
		}
		int z=lca(x,y);
		printf("%d\n",dianquan[z-n]);
	}
	return 0;
}