`M` is a matrix, represented as a list of lists, that has already been defined. The dimension of `M` is . Assume that both and are greater than or equal to and all elements of `M` are integers. Select all correct options about the code given below.
```
# M is a matrix (list of lists) that has already been defined
n = len(M[0])
flag = True
for i in range(n):
if M[0][i] - M[-1][i] != 1:
flag = False
print(flag)
```