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 int[] speak;

		private int aMask;
		private int aSize;

		private TestCase(int n, int m) {
			this.n = n;
			this.m = m;
			langs = new HashMap<String,Integer>(n);
			speak = new int[m];
			Arrays.fill(speak, 0);
		}

		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[i] |= 1 << lang;
				}
			}

			return testCase;
		}

		private void solve() {
			int aMask = 0;
			int aSize = 0;

			loop:
			for(int size = 1; size < Math.min(m, 6); size++) {
				for(int mask = (1 << size) - 1; mask < (1 << n); ) {
					if(isConnected(mask)) {
						aMask = mask;
						aSize = size;
						break loop;
					}

					int x = mask & ~(mask - 1);
					int y = mask + x;

					mask = y | ((mask & ~y) / x) >> 1;
				}
			}

			if(aMask == 0) {
				System.out.println("Impossible");
			}
			else {
				System.out.println(aSize);
				for(String lang : langs.keySet()) {
					if((aMask & (1 << langs.get(lang))) != 0)
						System.out.println(lang);
				}
			}
		}

		private void solve(int idx, int mask, int size) {
			if(size >= aSize)
				return;

			if(isConnected(mask)) {
				aMask = mask;
				aSize = size;
				return;
			}

			if(idx >= n)
				return;

			solve(idx + 1, mask, size);
			solve(idx + 1, mask | (1 << idx), size + 1);
		}

		private boolean isConnected(int mask) {
			int n0 = 0;
			int n1 = 1;
			int tmp = speak[0] & mask;
			int vis = 1;

			while(n0 < n1 && n1 < m) {
				n0 = n1;
				for(int i = 0; i < m; i++) {
					if((vis & (1 << i)) == 0 && (speak[i] & tmp) != 0) {
						vis |= 1 << i;
						tmp |= speak[i] & mask;
						n1++;
					}
				}
			}

			return n1 == m;
		}
	}
}