Verb phrases with two or more helping verbs always keep a definite order. Most helping verbs can combine with other helping verbs but will not combine with all of them. The examples below show good combinations.
has been said, will be said, could have been said, may have said, had been said
Instructions: 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.
1. am, will, being (fired)
2. been, could, does, have (learning)
3. might, do, have, been (sleeping)
4. must, were, be (discovered)
5. be, has, should (sold)
–For answers scroll down.
1. am being fired
2. could have been learning
3. might have been sleeping
4. must be discovered
5. should be sold
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from Daily Grammar Lessons Blog http://dailygrammarlessons.blogspot.com/2016/09/lesson-12-parts-of-speech-verbs.html