C中的2D动态内存分配数组

第一个问题解决了我可以使用*(*(矩阵i)j)

现在我又得到了另一个问题,最后的代码段是释放分配的内存(我也是从互联网上获得的),但我不明白,为什么我只能使用delete []矩阵？

int **matrix;

// dynamically allocate an array
matrix = new int *[row]; 
for (int count = 0; count < row; count++)
{
    matrix[count] = new int[col];
}

// input element for matrix
cout << endl << "Now enter the element for the matrix..."; 
for (int i=0; i < row; i++) 
{
    for (int j=0; j < col; j++)
    {
        cout << endl << "Row " << (i+1) << " Col " << (j+1) << " :";
        cin >> matrix[i][j]; // is there any equivalent declaration here?
    }
}

// free dynamically allocated memory
for( int i = 0 ; i < *row ; i++ )
{
    delete [] matrix[i] ;   
}
delete [] matrix ;