Flattening lists

What can be said about the codes A and B given below?

A:

[1, [2], 3]

|> List.flatten()

B:

[1, [2], 3]

v() |> List.flatten()

Options

1. Both A and B are equivalent.
2. Both A and B are not equivalent.
3. A will run without error but B will throw errors.
4. B will run without error but A will throw errors.