
Verbo regular: happen - happened - happened
Forma simple | Forma con V-ing | 
| - - it'd happen - - -  | - - it'd be happening - - -  | 
Perfecto | Perfecto con V-ing | 
| - - it would've happened - - -  | - - it would've been happening - - -  | 
Forma simple | Forma con V-ing | 
| - - it wouldn't happen - - -  | - - it wouldn't be happening - - -  | 
Perfecto | Perfecto con V-ing | 
| - - it wouldn't have happened - - -  | - - it wouldn't have been happening - - -  | 
Forma simple | Forma con V-ing | 
| - - would it happen? - - -  | - - would it be happening? - - -  | 
Perfecto | Perfecto con V-ing | 
| - - would it have happened? - - -  | - - would it have been happening? - - -  | 
Forma simple | Forma con V-ing | 
| - - wouldn't it happen? - - -  | - - wouldn't it be happening? - - -  | 
Perfecto | Perfecto con V-ing | 
| - - wouldn't it have happened? - - -  | - - wouldn't it have been happening? - - -  |