must biff
Regular verb: biff - biffed- biffed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must biff
you must biff
she must biff
we must biff
you must biff
they must biff 	I must be biffing
you must be biffing
she must be biffing
we must be biffing
you must be biffing
they must be biffing	I must have biffed
you must have biffed
she must have biffed
we must have biffed
you must have biffed
they must have biffed	I must have been biffing
you must have been biffing
she must have been biffing
we must have been biffing
you must have been biffing
they must have been biffing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not biff
you must not biff
she must not biff
we must not biff
you must not biff
they must not biff 	I must not be biffing
you must not be biffing
she must not be biffing
we must not be biffing
you must not be biffing
they must not be biffing	I must not have biffed
you must not have biffed
she must not have biffed
we must not have biffed
you must not have biffed
they must not have biffed	I must not have been biffing
you must not have been biffing
she must not have been biffing
we must not have been biffing
you must not have been biffing
they must not have been biffing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I biff?
must you biff?
must she biff?
must we biff?
must you biff?
must they biff? 	must I be biffing?
must you be biffing?
must she be biffing?
must we be biffing?
must you be biffing?
must they be biffing? 	must I have biffed?
must you have biffed?
must she have biffed?
must we have biffed?
must you have biffed?
must they have biffed? 	must I have been biffing?
must you have been biffing?
must she have been biffing?
must we have been biffing?
must you have been biffing?
must they have been biffing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I not biff?
must you not biff?
must she not biff?
must we not biff?
must you not biff?
must they not biff? 	must I not be biffing?
must you not be biffing?
must she not be biffing?
must we not be biffing?
must you not be biffing?
must they not be biffing? 	must I not have biffed?
must you not have biffed?
must she not have biffed?
must we not have biffed?
must you not have biffed?
must they not have biffed? 	must I not have been biffing?
must you not have been biffing?
must she not have been biffing?
must we not have been biffing?
must you not have been biffing?
must they not have been biffing?