#include <bits/stdc++.h>
using namespace std;
#define endl '\n'

const int maxn = 200010;

int n, m, N, rt, cnt, d, dv;
int ont[maxn], vis[maxn], dep[maxn], fa[maxn];
vector<int> e[maxn], g[maxn];
vector<int> ans;

char *p1,*p2,buf[100000];
#define nc() (p1==p2 && (p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++)
int read()
{
    int x=0,f=1;
    char ch=nc();
    while(ch<48||ch>57)
    {
        if(ch=='-')
            f=-1;
        ch=nc();
    }
    while(ch>=48&&ch<=57)
        x=x*10+ch-48,ch=nc();
   	return x*f;
}


void dfs0(int u) {
    ont[u] = 1;
    for(int v: e[u]) {
        if(ont[v]) continue;
        g[u].push_back(v);
        g[v].push_back(u);
        dfs0(v);
    }
}

void dfs1(int u, int f) {
    dep[u] = dep[f] + 1;
    if(!vis[u]) {
        if(dep[u] > d) {
            dv = u;
            d = dep[u];
        }
    }
    for(int v: g[u]) {
        if(v == f) continue;
        fa[v] = u;
        dfs1(v, u);
    }
}

void dfs2(int u, int f) {
    dep[u] = dep[f] + 1;
    if(dep[u] - 1 > N) {
        return;
    }
    if(dep[u] - 1 <= N && !vis[u]) {
        vis[u] = 1;
        cnt++;
    }
    for(int v: g[u]) {
        if(v == f) continue;
        dfs2(v, u);
    }
}

int climb(int u) {
    for(int i = 1; i <= N; i++) u = fa[u];
    return u;
}

mt19937 rd(time(0));

void solve() {
    ans.clear();
    cnt = 0;
    n = read();
    m = read();
    N = ceil(sqrt(n));
    for(int i = 1; i <= n; i++) {
        vis[i] = dep[i] = fa[i] = ont[i] = 0;
        e[i].clear();
        g[i].clear();
    }
    for(int i = 1; i <= m; i++) {
        int u, v;
        u = read();
        v = read();
        e[u].push_back(v);
        e[v].push_back(u);
    }
    int rt = rd() % n + 1;
    dfs0(rt);
    while(true) {
        assert(ans.size() <= n);
        if(cnt == n) break;
        fa[rt] = 0;
        d = 0;
        dfs1(rt, 0);
        if(d >= N + 1) {
            rt = climb(dv);
        }
        dfs2(rt, 0);
        ans.push_back(rt);
    }
    cout << ans.size() << endl;
    for(int v: ans) cout << v << " ";
    cout << endl; 
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int t = 1;
    t = read();
    while(t--) solve();
}