#include<bits/stdc++.h>

using namespace std;
#define int long long
int n, m;
const int N = 4e5 + 20, M = 3e6;
int head[N], ver[M * 2], nxt[M * 2];
int tot = 0;
queue<int> q;
vector<int> ans;
int d[N];
int k;
int v[N];
inline void add(int x, int y) {
	ver[++tot] = y;
	nxt[tot] = head[x];
	head[x] = tot;
}
void init() {
	ans.clear();
	tot = 0;
	for (int i = 0; i <= n; i++) {
		head[i] = 0;
		d[i] = 0;
		v[i] = 0;
	}
}
void dfs(int x){
	if(v[x])return;
	v[x] = 1;
	for(int _ = head[x]; _; _ = nxt[_]){
		int y = ver[_];
		if(v[y]) continue;
		dfs(y);
		d[x] = max(d[x], d[y] + 1);
	}
	if(d[x] >= k || x == 1) {
		d[x] = -1;
		ans.push_back(x);
	}

}
signed main()
{
	int T;
	cin >> T;
	while (T--) {
		scanf("%lld%lld", &n, &m);
		init();
		for (int i = 1; i <= m; i++) {
			int x, y;
			scanf("%lld%lld", &x, &y);
			add(x, y);
			add(y, x);
		}
		k = ceil(sqrt(n));
		dfs(1);
		//assert(ans.size() <= k);
		printf("%lld\n", (int)ans.size());
		for (int x : ans) {
			printf("%lld ", x);
		}
		puts("");
	}

	return 0;
}