#include<bits/stdc++.h>
using namespace std;
constexpr int M=2e5+5;
vector<int>ans,adj[M];
int n,m,blk,f[M],len[M];
int read(){
    int x=0;char ch=getchar();
    while (!isdigit(ch)) ch=getchar();
    while (isdigit(ch)) x=x*10+ch-48,ch=getchar();
    return x;
}
int find(int x){return f[x]==x?x:f[x]=find(f[x]);}
void dfs(int x,int f){
    len[x]=0;
    for (auto y:adj[x]){
        if (y==f) continue;
        dfs(y,x);len[x]=max(len[x],len[y]);
    }
    len[x]++;
    if (len[x]==blk||!f)
        ans.emplace_back(x),len[x]=0;
}
void solve(){
    n=read();m=read();
    blk=ceil(sqrt(n));
    for (int i=1;i<=n;i++) f[i]=i,adj[i].clear();
    for (int i=1;i<=m;i++){
        int x=read(),y=read();
        int fx=find(x),fy=find(y);
        if (fx==fy) continue; f[fx]=fy;
        adj[x].emplace_back(y);
        adj[y].emplace_back(x);
    }
    ans.clear();dfs(1,0);
    printf("%d\n",(int)ans.size());
    for (auto x:ans) printf("%d ",x);puts("");
}
int main(){int T=read();while (T--) solve();return 0;}