
Verbo regular: snow - snowed - snowed
Forma simple | Forma con V-ing | 
| - - it must snow - - -  | - - it must be snowing - - -  | 
Perfecto | Perfecto con V-ing | 
| - - it must have snowed - - -  | - - it must have been snowing - - -  | 
Forma simple | Forma con V-ing | 
| - - it must not snow - - -  | - - it must not be snowing - - -  | 
Perfecto | Perfecto con V-ing | 
| - - it must not have snowed - - -  | - - it must not have been snowing - - -  | 
Forma simple | Forma con V-ing | 
| - - must it snow? - - -  | - - must it be snowing? - - -  | 
Perfecto | Perfecto con V-ing | 
| - - must it have snowed? - - -  | - - must it have been snowing? - - -  | 
Forma simple | Forma con V-ing | 
| - - must it not snow? - - -  | - - must it not be snowing? - - -  | 
Perfecto | Perfecto con V-ing | 
| - - must it not have snowed? - - -  | - - must it not have been snowing? - - -  |