English verb conjugation MUST HAPPEN
Regular verb: happen - happened - happened
Affirmation
Simple form
--
it must happen
-
-
-
V-ing form
--
it must be happening
-
-
-
Perfect
--
it must have happened
-
-
-
V-ing perfect
--
it must have been happening
-
-
-
Negation
Simple form
--
it must not happen
-
-
-
V-ing form
--
it must not be happening
-
-
-
Perfect
--
it must not have happened
-
-
-
V-ing perfect
--
it must not have been happening
-
-
-
Interrogative form
Simple form
--
must it happen?
-
-
-
V-ing form
--
must it be happening?
-
-
-
Perfect
--
must it have happened?
-
-
-
V-ing perfect
--
must it have been happening?
-
-
-
Interro-negative form
Simple form
--
must it not happen?
-
-
-
V-ing form
--
must it not be happening?
-
-
-
Perfect
--
must it not have happened?
-
-
-
V-ing perfect
--
must it not have been happening?
-
-
-