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

int dep[N], height[N],ans[N];
void dfs(int x, int fa)
{
	dep[x] = dep[fa]+1;
	height[x] = 0;
	for(int y : e[x]) {
		if(y == fa) continue;
		dfs(y, x);
		height[x] = max(height[x], height[y]+1);
	}
	if(height[x]==k){
		height[x]=-1;
		ans[++cnt]=x;
	}
}

int dis[N];

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

	int T; cin >> T;
	while(T--) {
		cnt=0;
		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);
		}
		k = sqrt(n);
		if(k*k < n) k++;
		dfs(1, 0);

		//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);
		}*/
		if(cnt < k && ans[cnt] != 1) ans[++cnt]=1;
		if(cnt > k) assert(0);

		for(int i = 0; i <= n; i++) dis[i] = 1e9;
		queue<int> q;
		for(int i = 1; i <= cnt; i++) {
			dis[ans[i]] = 0;
			q.push(ans[i]);
		}

		while(q.size()) {
			int x = q.front(); q.pop();
			// _debugVar(x);
			for(int y : e[x]) {
				if(dis[y] > dis[x]+1) {
					dis[y] = dis[x]+1;
					q.push(y);
				}
			}
		}

		for(int i = 1; i <= n; i++) 
			if(dis[i] > k) assert(0);

		cout << cnt << endl;
		for(int i=1;i<=cnt;i++) printf("%d ", ans[i]);
		puts("");
		for(int i=1;i<=n;i++) e[i].clear();
	}
	return 0;
}