import java.io.*;
import java.util.*;

public class party_yuizumi {
	public static void main(String[] args) throws Exception {
		Scanner cin = new Scanner(System.in);
		TestCase testCase;
		boolean isFirstCase = true;
		while((testCase = TestCase.scan(cin)) != null) {
			if(!isFirstCase) System.out.println();
			isFirstCase = false;
			testCase.solve();
		}
	}

	private static class TestCase {
		private int n;
		private int m;

		private Map<String,Integer> langs;
		private boolean[][] speak;

		private TestCase(int n, int m) {
			this.n = n;
			this.m = m;

			langs = new HashMap<String,Integer>(n);
			speak = new boolean[n][m];

			for(int i = 0; i < n; i++) {
				for(int j = 0; j < m; j++) {
					speak[i][j] = false;
				}
			}
		}

		private static TestCase scan(Scanner cin) {
			int n = cin.nextInt();
			int m = cin.nextInt();

			if(n == 0 && m == 0)
				return null;

			TestCase testCase = new TestCase(n, m);

			for(int i = 0; i < n; i++) {
				testCase.langs.put(cin.next(), i);
			}

			for(int i = 0; i < m; i++) {
				int k = cin.nextInt();
				for(int j = 0; j < k; j++) {
					int lang = testCase.langs.get(cin.next());
					testCase.speak[lang][i] = true;
				}
			}

			return testCase;
		}

		private void solve() {
			boolean[] use = new boolean[n];

			for(int i = 1; i < 6; i++) {
				Arrays.fill(use, false);

				if(search(use, i, 0)) {
					System.out.println(i);
					for(String lang : langs.keySet()) {
						if(use[langs.get(lang)]) System.out.println(lang);
					}
					return;
				}
			}

			System.out.println("Impossible");
		}

		private boolean search(boolean[] use, int size, int idx) {
			if(size == 0) {
				return isConnected(use);
			}

			if(idx >= n)
				return false;

			use[idx] = true;
			if(search(use, size - 1, idx + 1)) return true;
			use[idx] = false;
			if(search(use, size - 0, idx + 1)) return true;
			return false;
		}

		private boolean isConnected(boolean[] use) {
			boolean[] vis = new boolean[m];
			Arrays.fill(vis, false);
			traverse(use, vis, 0);
			for(int i = 1; i < m; i++) { if(!vis[i]) return false; }
			return true;
		}

		private void traverse(boolean[] use, boolean[] vis, int idx) {
			vis[idx] = true;

			for(int i = 1; i < m; i++) {
				if(vis[i]) continue;
				for(int j = 0; j < n; j++) {
					if(use[j] && speak[j][idx] && speak[j][i])
						traverse(use, vis, i);
				}
			}
		}
	}
}