Regular verb: happen - happened - happened
Simple form | V-ing form |
- - it should happen - - - | - - it should be happening - - - |
Perfect | V-ing perfect |
- - it should have happened - - - | - - it should have been happening - - - |
Simple form | V-ing form |
- - it should not happen - - - | - - it should not be happening - - - |
Perfect | V-ing perfect |
- - it should not have happened - - - | - - it should not have been happening - - - |
Simple form | V-ing form |
- - should it happen? - - - | - - should it be happening? - - - |
Perfect | V-ing perfect |
- - should it have happened? - - - | - - should it have been happening? - - - |
Simple form | V-ing form |
- - should it not happen? - - - | - - should it not be happening? - - - |
Perfect | V-ing perfect |
- - should it not have happened? - - - | - - should it not have been happening? - - - |