#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

// #define tpyeinput int
// inline char nc() {static char buf[1000000],*p1=buf,*p2=buf;return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;}
// inline void read(tpyeinput &sum) {char ch=nc();sum=0;while(!(ch>='0'&&ch<='9')) ch=nc();while(ch>='0'&&ch<='9') sum=(sum<<3)+(sum<<1)+(ch-48),ch=nc();}

template<typename T>
void read(T &x) {
    int f = 1;
    x = 0;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = x * 10 + (ch ^ 48);
        ch = getchar();
    }
    x *= f;
}

const int N = 1e6+10, M = 2*N;
vector<int> g[N];
vector<int> ans;
int n, m, k;
int dep[N];
int rand(int l, int r) {
    return (ll)rand()*rand() % (r - l + 1) + l;
}

bool bfs(int u) {
    ans.clear();
    queue<pair<int, int>> q;
    for(int i=1; i<=n; i++) dep[i] = 0;
    q.push({u, dep[u] = 1});
    while(!q.empty()) {
        auto x = q.front().first, d = q.front().second;
        q.pop();
        for (auto v : g[x]) {
            if(dep[v]) continue;
            q.push({v, dep[v] = d+1});
        }
    }
    for(int i=1; i<=n; i++) {
        if(dep[i] % (k+1) == 1) ans.push_back(i);
    }
    if(ans.size() <= k) return true;
    return false;
}

void solve() {
    read(n); read(m); 
    k = ceil(sqrt(n));
    for(int i=1; i<=n; i++) g[i].clear(); 
    for(int i=1; i<=m; i++) {
        int u, v;
        read(u); read(v);
        g[u].push_back(v);
        g[v].push_back(u);
    }
    while(!bfs(rand(1, n)));
    printf("%d\n", ans.size());
    for(auto x : ans) printf("%d ", x); puts("");

}


int main() {
#ifdef LOCAL_TEST
    freopen("test.in", "r", stdin);
#endif
    srand(time(0));
    int times = 1;
    read(times);
    while(times--) {
        solve();
    }
    return 0;
}