Between 3 and 4 is basically a formality thing. The -zu negative is a formal written thing (a leftover from classical japanese) where 'zu ni' means 'naide' and 'zu' means 'nai', and various grammar patterns can use either.
For JLPT and similar test purposes you won't get questions that give you two interchangeable answers -- but they do like to ask questions where the context means only one choice is possible, or where the following particle or the verb tense means one answer won't fit.
For JLPT and similar test purposes you won't get questions that give you two interchangeable answers -- but they do like to ask questions where the context means only one choice is possible, or where the following particle or the verb tense means one answer won't fit.