must crack
Regular verb: crack - cracked- cracked

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must crack
you must crack
he must crack
we must crack
you must crack
they must crack 	I must be cracking
you must be cracking
he must be cracking
we must be cracking
you must be cracking
they must be cracking	I must have cracked
you must have cracked
he must have cracked
we must have cracked
you must have cracked
they must have cracked	I must have been cracking
you must have been cracking
he must have been cracking
we must have been cracking
you must have been cracking
they must have been cracking	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't crack
you mustn't crack
he mustn't crack
we mustn't crack
you mustn't crack
they mustn't crack 	I mustn't be cracking
you mustn't be cracking
he mustn't be cracking
we mustn't be cracking
you mustn't be cracking
they mustn't be cracking	I mustn't have cracked
you mustn't have cracked
he mustn't have cracked
we mustn't have cracked
you mustn't have cracked
they mustn't have cracked	I mustn't have been cracking
you mustn't have been cracking
he mustn't have been cracking
we mustn't have been cracking
you mustn't have been cracking
they mustn't have been cracking	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I crack?
must you crack?
must he crack?
must we crack?
must you crack?
must they crack? 	must I be cracking?
must you be cracking?
must he be cracking?
must we be cracking?
must you be cracking?
must they be cracking? 	must I have cracked?
must you have cracked?
must he have cracked?
must we have cracked?
must you have cracked?
must they have cracked? 	must I have been cracking?
must you have been cracking?
must he have been cracking?
must we have been cracking?
must you have been cracking?
must they have been cracking? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I crack?
mustn't you crack?
mustn't he crack?
mustn't we crack?
mustn't you crack?
mustn't they crack? 	mustn't I be cracking?
mustn't you be cracking?
mustn't he be cracking?
mustn't we be cracking?
mustn't you be cracking?
mustn't they be cracking? 	mustn't I have cracked?
mustn't you have cracked?
mustn't he have cracked?
mustn't we have cracked?
mustn't you have cracked?
mustn't they have cracked? 	mustn't I have been cracking?
mustn't you have been cracking?
mustn't he have been cracking?
mustn't we have been cracking?
mustn't you have been cracking?
mustn't they have been cracking?