#include<bits/stdc++.h>
using namespace std;
const int maxn=2e6+5;

struct Edge
{
    int next;int to;
}edge[maxn];
int dep[maxn],n,sqn,head[maxn],cnt,m;
bool sel[maxn],vis[maxn];
void addedge(int from,int to)
{
    edge[++cnt].next=head[from];
    edge[cnt].to=to;
    head[from]=cnt;
}
int dfs(int u,int fat)
{
    //返回值为所能访问到的节点的最大深度
    vis[u]=true;
    dep[u]=dep[fat]+1;
    int maxdep=dep[u];
    for(int i=head[u];i;i=edge[i].next)
    {
        int v=edge[i].to;
        if(v==fat||vis[v]) continue;
        int tmp=dfs(v,u);
        maxdep=max(maxdep,tmp);
    }
    //printf("dep[%d]=%d,maxdep=%d\n",u,dep[u],maxdep);
    if(maxdep-dep[u]==sqn)
    {
        sel[u]=true;
        return 0;
    }
    else return maxdep;
}
vector<int> ans;
void work()
{
    cin>>n>>m;
    if(n/sqrt(n)==sqrt(n)) sqn=sqrt(n);
    else sqn=(int)sqrt(n)+1;
    //printf("sqn=%d\n",sqn);
    for(int i=1;i<=m;i++)
    {
        int x,y;
        cin>>x>>y;
        addedge(x,y);
        addedge(y,x);
    }
    dep[0]=0;
    dfs(1,0);
    if(ans.size()<sqn) sel[1]=true;
        
    for(int i=1;i<=n;i++)
        if(sel[i]) ans.push_back(i),sel[i]=false;

    cout<<ans.size()<<'\n';
    for(auto item:ans)
        cout<<item<<' ';
    cout<<'\n';
    for(int i=1;i<=n;i++) vis[i]=false,head[i]=0;
    for(int i=1;i<=cnt;i++) edge[i].next=0;
    cnt=0;ans.clear();
}
int main()
{
	cin.tie(0);
	cin.sync_with_stdio(0);
	int t=1;
	cin>>t;
	while(t--)
		work();
	return 0;
}