Arrange the following helping verbs with the word in parentheses into a verb phrase. One of the helping verbs will not combine and must be left out. Example: was, have, may (gone) = may have gone - was will not combine in this group. Which of the following options correctly arranges the helping verbs with the word 'discovered'?
1) must be discovered
2) were be discovered
3) discovered must be
4) be discovered were