I must nibble you must nibble he must nibble we must nibble you must nibble they must nibble
V-ing form
I must be nibbling you must be nibbling he must be nibbling we must be nibbling you must be nibbling they must be nibbling
Perfect
I must have nibbled you must have nibbled he must have nibbled we must have nibbled you must have nibbled they must have nibbled
V-ing perfect
I must have been nibbling you must have been nibbling he must have been nibbling we must have been nibbling you must have been nibbling they must have been nibbling
Negation
Simple form
I mustn't nibble you mustn't nibble he mustn't nibble we mustn't nibble you mustn't nibble they mustn't nibble
V-ing form
I mustn't be nibbling you mustn't be nibbling he mustn't be nibbling we mustn't be nibbling you mustn't be nibbling they mustn't be nibbling
Perfect
I mustn't have nibbled you mustn't have nibbled he mustn't have nibbled we mustn't have nibbled you mustn't have nibbled they mustn't have nibbled
V-ing perfect
I mustn't have been nibbling you mustn't have been nibbling he mustn't have been nibbling we mustn't have been nibbling you mustn't have been nibbling they mustn't have been nibbling
Interrogative form
Simple form
must I nibble? must you nibble? must he nibble? must we nibble? must you nibble? must they nibble?
V-ing form
must I be nibbling? must you be nibbling? must he be nibbling? must we be nibbling? must you be nibbling? must they be nibbling?
Perfect
must I have nibbled? must you have nibbled? must he have nibbled? must we have nibbled? must you have nibbled? must they have nibbled?
V-ing perfect
must I have been nibbling? must you have been nibbling? must he have been nibbling? must we have been nibbling? must you have been nibbling? must they have been nibbling?
Interro-negative form
Simple form
mustn't I nibble? mustn't you nibble? mustn't he nibble? mustn't we nibble? mustn't you nibble? mustn't they nibble?
V-ing form
mustn't I be nibbling? mustn't you be nibbling? mustn't he be nibbling? mustn't we be nibbling? mustn't you be nibbling? mustn't they be nibbling?
Perfect
mustn't I have nibbled? mustn't you have nibbled? mustn't he have nibbled? mustn't we have nibbled? mustn't you have nibbled? mustn't they have nibbled?
V-ing perfect
mustn't I have been nibbling? mustn't you have been nibbling? mustn't he have been nibbling? mustn't we have been nibbling? mustn't you have been nibbling? mustn't they have been nibbling?