Question

You can't enter the exposition ......... you buy a ticket 1) when 2) unless 3) if 4) while P. S. Возможны несколько вариантов ответа (даже 4). Также возможно, что правильного ответа нет

Answer 1

Unless...........................

Answer 2

You can't enter the exposition unless you buy a ticket. This means that you are not allowed to enter the exposition unless you have purchased a ticket. So, the correct answer is 2) unless.