#include <bits/stdc++.h>

#define _debugVar(x) { cerr << #x << " = " << x << endl; }

using namespace std;
using LL = long long;

const int N = 2e5+5;

int n, m, k;
vector<int> e[N];

int par[N];
int Find(int x) { return (par[x] == x) ? x : par[x] = Find(par[x]); }

int dep[N], height[N];
void dfs(int x, int fa)
{
	dep[x] = dep[fa]+1;
	height[x] = 1;
	for(int y : e[x]) {
		if(y == fa) continue;
		dfs(y, x);
		height[x] = max(height[x], height[y]+1);
	}
}

int main()
{
	// freopen("1.in", "r", stdin);
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int T; cin >> T;
	while(T--) {
		cin >> n >> m;
		for(int i = 1; i <= n; i++) {
			e[i].clear();
			par[i] = i;
		}
		for(int i = 1; i <= m; i++) {
			int x, y;
			cin >> x >> y;
			if(Find(x) == Find(y)) continue;
			par[Find(x)] = Find(y);
			e[x].push_back(y); e[y].push_back(x);
		}

		dfs(1, 0);

		k = sqrt(n);
		if(k*k < n) k++;

		vector<int> ans;
		for(int i = 1; i <= n; i++) {
			// if(dep[i]%(k+1) == 1) ans.push_back(i);
			if(height[i]%(k+1) == 0) ans.push_back(i);
		}
		if((int)ans.size() < k) {
			if(ans.size() == 0 || (ans[0] != 1))
				ans.push_back(1);
		}
		cout << ans.size() << endl;
		for(int x : ans) printf("%d ", x);
		puts("");
	}
	return 0;
}