Aren't the same?

[Sillierjarl]

Are not answer 2 and 4 the same?

[lopicake]

You can’t use the ます form with です. So 4 is ungrammatical.

Here’s an explanation.

I was wrong.

[Naphthalene]

The correct answer is 4 though

[ctmf]

I’m not… seeing how that link answers the question. So which answer is correct?

Is not arimasen deshita the preferred polite past negative?

(actually I think じゃなかったです sounds right, but that’s not an option.)

edit: answered by @Naphthalene

[lopicake]

Lol I saw it as です not でした。This is why I don’t answer questions. Whoops.

[acm2010]

You normally don’t combine verbs and です, but the negative form ません comes from the old ぬ negation style, which is not compatible with past た, so you need a “helper” でした.