Consider this argument: 'Whenever the shop runs a weekend offer, its takings for the week rise. The shop's takings rose last week. So the shop must have run a weekend offer.' Which of the following contains the same error in reasoning?

The original argues backwards from an outcome to one thing that would have produced it, ignoring that other things might have produced it too - takings can rise for many reasons. The pond argument repeats that mistake exactly, since an overflow could equally follow an upstream release. The first option is also faulty, but its error is the different one of denying the condition; the last two are valid.