#include <vector>
#include <sstream>
#include <algorithm>
#include <fstream>
#include <list>
#include <unordered_map>
#include <map>
#include <istream>
#include <sstream>
#include <stack>
#include <ctime>
#include <stdio.h>
#include <set>
#include <cmath>
#include <bitset>
#include <iostream>
#include <iomanip>
#include <queue>
#include <string>

#define endl "\n"
/*#define all(x) x.begin(),x.end()
#define rr return 0
#define xx first
#define yy second
#define pii pair<int,int>
#define lcm(a,b) a*b/gcd(a,b)*/

using namespace std;

typedef long long ll;
typedef long double ld;


signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t;
    int r, c, h, v;
    cin >> t;
    int pp = 1;
    vector<vector<char>> a;
    vector<int> rows;
    vector<int> cols;
    while(t){
        cin >> r >> c >> h >> v;
        a.resize(r);
        rows.resize(r);
        cols.resize(c);
        string s;
        int ch = 0;
        for(int i = 0;i < r;i++){
            a[i].resize(c);
            cin >> s;
            for(int j = 0;j < c;j++){
                a[i][j] = s[j];
                if(a[i][j] == '@'){
                    ch++;
                }
            }
        }
        int num = (h + 1) * (v + 1);
        if(ch == 0){
            cout << "Case #" << pp << ": ";
            pp++;
            cout << "POSSIBLE" << endl;
            continue;
        }
        int numc, numr;
        numc = ch / (v + 1);
        numr = ch / (h + 1);
        bool ok = true;
        if(ch % num != 0){
            ok = 0;
        }
        int inone = ch / num;
        for(int i = 0;i < r;i++){
            int u = 0;
            for(int j = 0;j < c;j++){
                if(a[i][j] == '@'){
                    u++;
                }
            }
            rows[i] = u;
        }
        for(int i = 0;i < c;i++){
            int u = 0;
            for(int j = 0;j < r;j++){
                if(a[j][i] == '@'){
                    u++;
                }
            }
            cols[i] = u;
        }
        int tmp = 0;
        int cs = 0;
        vector<int> colR;
        for(int i = 0;i < c;i++){
            tmp += cols[i];
            if(tmp > numc){
                ok = 0;
            }else if(tmp == numc){
                tmp = 0;
                cs++;
                if((i + 1) >= 0 && (i + 1) < c)
                    colR.push_back(i + 1);
            }else if(i == c-1 && tmp < numc){
                ok = 0;
            }
        }
        colR.push_back(c);
        int rs = 0;
        int prevRaz = 0;
        tmp = 0;
        for(int i = 0;i < r;i++){
            tmp += rows[i];
            if(tmp > numr){
                ok = 0;
            }else if(tmp == numr){
                int ch1 = 0;
                int prev = 0;
                for(int j : colR){
                    ch1 = 0;
                    for(int z = prevRaz;z <= i;z++){
                        for(int k = prev;k < j;k++){
                            if(a[z][k] == '@'){
                                ch1++;
                            }
                        }
                    }
                    prev = j;
                    if(ch1 != inone){
                        ok = 0;
                        break;
                    }
                }
                if(!ok){
                    break;
                }
                tmp = 0;
                rs++;
                prevRaz = i + 1;
            }else if(i == r-1 && tmp < numr){
                ok = 0;
            }
        }
        if(cs != (v + 1) && rs != (h + 1)){
            ok = 0;
        }
        cout << "Case #" << pp << ": ";
        if(ok)
            cout << "POSSIBLE" << endl;
        else
            cout << "IMPOSSIBLE" << endl;
        --t;
        pp++;
        colR.clear();
    }
    return 0;
}