
Verbo irregular: freeze - froze - frozen
Forma simple | Forma con V-ing | 
| - - it must freeze - - -  | - - it must be freezing - - -  | 
Perfecto | Perfecto con V-ing | 
| - - it must have frozen - - -  | - - it must have been freezing - - -  | 
Forma simple | Forma con V-ing | 
| - - it must not freeze - - -  | - - it must not be freezing - - -  | 
Perfecto | Perfecto con V-ing | 
| - - it must not have frozen - - -  | - - it must not have been freezing - - -  | 
Forma simple | Forma con V-ing | 
| - - must it freeze? - - -  | - - must it be freezing? - - -  | 
Perfecto | Perfecto con V-ing | 
| - - must it have frozen? - - -  | - - must it have been freezing? - - -  | 
Forma simple | Forma con V-ing | 
| - - must it not freeze? - - -  | - - must it not be freezing? - - -  | 
Perfecto | Perfecto con V-ing | 
| - - must it not have frozen? - - -  | - - must it not have been freezing? - - -  |