must countersign
Regular verb: countersign - countersigned- countersigned

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must countersign
you must countersign
she must countersign
we must countersign
you must countersign
they must countersign 	I must be countersigning
you must be countersigning
she must be countersigning
we must be countersigning
you must be countersigning
they must be countersigning	I must have countersigned
you must have countersigned
she must have countersigned
we must have countersigned
you must have countersigned
they must have countersigned	I must have been countersigning
you must have been countersigning
she must have been countersigning
we must have been countersigning
you must have been countersigning
they must have been countersigning	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't countersign
you mustn't countersign
she mustn't countersign
we mustn't countersign
you mustn't countersign
they mustn't countersign 	I mustn't be countersigning
you mustn't be countersigning
she mustn't be countersigning
we mustn't be countersigning
you mustn't be countersigning
they mustn't be countersigning	I mustn't have countersigned
you mustn't have countersigned
she mustn't have countersigned
we mustn't have countersigned
you mustn't have countersigned
they mustn't have countersigned	I mustn't have been countersigning
you mustn't have been countersigning
she mustn't have been countersigning
we mustn't have been countersigning
you mustn't have been countersigning
they mustn't have been countersigning	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I countersign?
must you countersign?
must she countersign?
must we countersign?
must you countersign?
must they countersign? 	must I be countersigning?
must you be countersigning?
must she be countersigning?
must we be countersigning?
must you be countersigning?
must they be countersigning? 	must I have countersigned?
must you have countersigned?
must she have countersigned?
must we have countersigned?
must you have countersigned?
must they have countersigned? 	must I have been countersigning?
must you have been countersigning?
must she have been countersigning?
must we have been countersigning?
must you have been countersigning?
must they have been countersigning? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I countersign?
mustn't you countersign?
mustn't she countersign?
mustn't we countersign?
mustn't you countersign?
mustn't they countersign? 	mustn't I be countersigning?
mustn't you be countersigning?
mustn't she be countersigning?
mustn't we be countersigning?
mustn't you be countersigning?
mustn't they be countersigning? 	mustn't I have countersigned?
mustn't you have countersigned?
mustn't she have countersigned?
mustn't we have countersigned?
mustn't you have countersigned?
mustn't they have countersigned? 	mustn't I have been countersigning?
mustn't you have been countersigning?
mustn't she have been countersigning?
mustn't we have been countersigning?
mustn't you have been countersigning?
mustn't they have been countersigning?