#include<cstdio>

#include<cstring>

using namespace std;

int n,m,K,T;

bool a[30][30];

int main(){

	freopen("figure.in","r",stdin);

	freopen("figure.out","w",stdout);

	scanf("%d",&T);

	for(int zu=1;zu<=T;++zu){

		memset(a,0,sizeof(a));

		scanf("%d%d%d",&n,&m,&K);

		if(K>((n-2)*(m-2)+1)/2 || n<=2 || m<=2){

			puts("Impossible");

		}

		else{

			int pen,cnt=0;

			for(int i=2;i<n;++i){

				pen=i;

				for(int j=2;j<m;++j){

					++pen;

					if(pen&1){

						++cnt;

						a[i][j]=1;

						if(cnt==K){

							goto OUT;

						}

					}

				}

			}

			OUT:

				for(int i=1;i<=n;++i){

					for(int j=1;j<=m;++j){

						if(a[i][j]){

							putchar('#');

						}

						else{

							putchar('.');

						}

					}

					puts("");

				}

		}

		if(zu!=T){

			puts("");

		}

	}

	return 0;

}