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