I must crack you must crack he must crack we must crack you must crack they must crack
V-ing form
I must be cracking you must be cracking he must be cracking we must be cracking you must be cracking they must be cracking
Perfect
I must have cracked you must have cracked he 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 he must have been cracking we must have been cracking you must have been cracking they must have been cracking
Negation
Simple form
I must not crack you must not crack he must not crack we must not crack you must not crack they must not crack
V-ing form
I must not be cracking you must not be cracking he must not be cracking we must not be cracking you must not be cracking they must not be cracking
Perfect
I must not have cracked you must not have cracked he must not have cracked we must not have cracked you must not have cracked they must not have cracked
V-ing perfect
I must not have been cracking you must not have been cracking he must not have been cracking we must not have been cracking you must not have been cracking they must not have been cracking
Interrogative form
Simple form
must I crack? must you crack? must he crack? must we crack? must you crack? must they crack?
V-ing form
must I be cracking? must you be cracking? must he be cracking? must we be cracking? must you be cracking? must they be cracking?
Perfect
must I have cracked? must you have cracked? must he 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 he have been cracking? must we have been cracking? must you have been cracking? must they have been cracking?
Interro-negative form
Simple form
must I not crack? must you not crack? must he not crack? must we not crack? must you not crack? must they not crack?
V-ing form
must I not be cracking? must you not be cracking? must he not be cracking? must we not be cracking? must you not be cracking? must they not be cracking?
Perfect
must I not have cracked? must you not have cracked? must he not have cracked? must we not have cracked? must you not have cracked? must they not have cracked?
V-ing perfect
must I not have been cracking? must you not have been cracking? must he not have been cracking? must we not have been cracking? must you not have been cracking? must they not have been cracking?