must nibble
Regular verb: nibble - nibbled- nibbled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must nibble
you must nibble
she must nibble
we must nibble
you must nibble
they must nibble 	I must be nibbling
you must be nibbling
she must be nibbling
we must be nibbling
you must be nibbling
they must be nibbling	I must have nibbled
you must have nibbled
she must have nibbled
we must have nibbled
you must have nibbled
they must have nibbled	I must have been nibbling
you must have been nibbling
she must have been nibbling
we must have been nibbling
you must have been nibbling
they must have been nibbling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not nibble
you must not nibble
she must not nibble
we must not nibble
you must not nibble
they must not nibble 	I must not be nibbling
you must not be nibbling
she must not be nibbling
we must not be nibbling
you must not be nibbling
they must not be nibbling	I must not have nibbled
you must not have nibbled
she must not have nibbled
we must not have nibbled
you must not have nibbled
they must not have nibbled	I must not have been nibbling
you must not have been nibbling
she must not have been nibbling
we must not have been nibbling
you must not have been nibbling
they must not have been nibbling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I nibble?
must you nibble?
must she nibble?
must we nibble?
must you nibble?
must they nibble? 	must I be nibbling?
must you be nibbling?
must she be nibbling?
must we be nibbling?
must you be nibbling?
must they be nibbling? 	must I have nibbled?
must you have nibbled?
must she have nibbled?
must we have nibbled?
must you have nibbled?
must they have nibbled? 	must I have been nibbling?
must you have been nibbling?
must she have been nibbling?
must we have been nibbling?
must you have been nibbling?
must they have been nibbling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I not nibble?
must you not nibble?
must she not nibble?
must we not nibble?
must you not nibble?
must they not nibble? 	must I not be nibbling?
must you not be nibbling?
must she not be nibbling?
must we not be nibbling?
must you not be nibbling?
must they not be nibbling? 	must I not have nibbled?
must you not have nibbled?
must she not have nibbled?
must we not have nibbled?
must you not have nibbled?
must they not have nibbled? 	must I not have been nibbling?
must you not have been nibbling?
must she not have been nibbling?
must we not have been nibbling?
must you not have been nibbling?
must they not have been nibbling?