#include<bits/stdc++.h>

using namespace std;
int n, m;
const int N = 2e5+20, M = 1.2e6;
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[1] = 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);
		}
	}
}
int main()
{
	int T;
	cin >> T;
	while(T--){
		vector<int> ans;
		scanf("%d%d", &n, &m);
		init();
		for(int i = 1; i <= m; i++){
			int x, y;
			scanf("%d%d", &x, &y);
			add(x, y);
			add(y, x);
		}
		bfs(1);
		//for(int i = 1; i <= n; i++) cout << d[i] << "  ";
		int k = ceil(sqrt(n));
		for(int i = 1; i <= n; i++){
			if(d[i] % (k+1) == 0){
				ans.push_back(i);
			}
		}
		printf("%d\n", (int)ans.size());
		for(int x : ans){
			printf("%d ", x);
		}
		puts("");
	}

	return 0;
}