#include <bits/stdc++.h>
using namespace std;
inline int read()
{
	char ch;
	while((ch=getchar())<'0'||ch>'9');
	int res=ch-'0';
	while((ch=getchar())>='0'&&ch<='9') res=res*10+ch-'0';
	return res;
}	
const int N=200100;
struct Edge{
	int nxt,to;
}e[N<<1];
int h[N],e_num;
void add(int from,int to)
{
	e[++e_num].nxt=h[from];
	e[e_num].to=to;
	h[from]=e_num;
}
int n,K;
struct BCJ{
	int f[N];
	void pre()
	{
		for(int i=1;i<=n;i++) 
			f[i]=i;
	}
	int find(int x){ return f[x]==x?x:(f[x]=find(f[x])); }
	bool mrge(int x,int y)
	{
		x=find(x),y=find(y);
		if(x==y) return 0;
		f[x]=y;
		return 1;
	}
}B;
int res[N],ans,vis[N];
int dep[N];
struct node{
	int dep,u;
	node(int a=0,int b=0){
		u=a,dep=b;
	}
};
bool operator<(node a,node b){ return a.dep<b.dep; }
priority_queue<node>Q;
int stk[N],top,fa[N];
void dfs(int u)
{
	stk[++top]=u;Q.push(node(u,dep[u]));
	if(top>K) fa[u]=stk[top-K];
	else fa[u]=1;
	for(int i=h[u];i;i=e[i].nxt)
	{
		int v=e[i].to;
		if(dep[v]) continue;
		dep[v]=dep[u]+1;
		dfs(v);
	}
	top--;
}
void dfs_vis(int u)
{
	vis[u]=1;
	for(int i=h[u];i;i=e[i].nxt)
	{
		int v=e[i].to;
		if(vis[v]||dep[v]<dep[u]) continue;
		dfs_vis(v);
	}
}
int main()
{
	int T=read();
	while(T--)
	{
		n=read();int m=read();
		B.pre();
		e_num=0;
		ans=0;
		for(int i=1;i<=n;i++) vis[i]=h[i]=0;
		for(int i=1;i<=m;i++)
		{
			int u=read(),v=read();
			if(B.mrge(u,v)) add(u,v),add(v,u);
		}
		K=sqrt(n);
		if(K*K!=n) K++;
		assert(K*K>=n);
		dep[1]=1;dfs(1);
		while(!Q.empty())
		{
			node tmp=Q.top();Q.pop();
			int u=tmp.u;
			if(vis[u]) continue;
			dfs_vis(fa[u]);
			res[++ans]=fa[u];
		}
		printf("%d\n",ans);
		for(int i=1;i<=ans;i++) printf("%d ",res[i]);
		printf("\n");
	}
	return 0;
}