#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;
int d[N];
inline void add(int x, int y) {
	ver[++tot] = y;
	nxt[tot] = head[x];
	head[x] = tot;
}
void init() {
	tot = 0;
	for (int i = 0; i <= n; i++) {
		head[i] = 0;
		d[i] = -1;
	}
}
void bfs(int fir) {
	q.push(fir);
	d[fir] = 0;
	while (q.size()) {
		int x = q.front();
		q.pop();
		for (int _ = head[x]; _; _ = nxt[_]) {
			int y = ver[_];
			if (d[y] != -1) continue;
			d[y] = d[x] + 1;
			q.push(y);
		}
	}
}
signed main()
{
	int T;
	cin >> T;
	while (T--) {
		vector<int> ans;
		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);
		}
		bfs(1);
		int k = ceil(sqrt(n));
		for (int i = 1; i <= n; i++) {
			//cout << d[i] << " ";
			if (d[i] % (k + 1) == 0) {
				ans.push_back(i);
			}
		}
		//cout << endl;
		assert(ans.size() <= k);
		printf("%lld\n", (int)ans.size());
		for (int x : ans) {
			printf("%lld ", x);
		}
		puts("");
	}

	return 0;
}