I must crackle you must crackle he must crackle we must crackle you must crackle they must crackle
V-ing form
I must be crackling you must be crackling he must be crackling we must be crackling you must be crackling they must be crackling
Perfect
I must have crackled you must have crackled he must have crackled we must have crackled you must have crackled they must have crackled
V-ing perfect
I must have been crackling you must have been crackling he must have been crackling we must have been crackling you must have been crackling they must have been crackling
Negation
Simple form
I must not crackle you must not crackle he must not crackle we must not crackle you must not crackle they must not crackle
V-ing form
I must not be crackling you must not be crackling he must not be crackling we must not be crackling you must not be crackling they must not be crackling
Perfect
I must not have crackled you must not have crackled he must not have crackled we must not have crackled you must not have crackled they must not have crackled
V-ing perfect
I must not have been crackling you must not have been crackling he must not have been crackling we must not have been crackling you must not have been crackling they must not have been crackling
Interrogative form
Simple form
must I crackle? must you crackle? must he crackle? must we crackle? must you crackle? must they crackle?
V-ing form
must I be crackling? must you be crackling? must he be crackling? must we be crackling? must you be crackling? must they be crackling?
Perfect
must I have crackled? must you have crackled? must he have crackled? must we have crackled? must you have crackled? must they have crackled?
V-ing perfect
must I have been crackling? must you have been crackling? must he have been crackling? must we have been crackling? must you have been crackling? must they have been crackling?
Interro-negative form
Simple form
must I not crackle? must you not crackle? must he not crackle? must we not crackle? must you not crackle? must they not crackle?
V-ing form
must I not be crackling? must you not be crackling? must he not be crackling? must we not be crackling? must you not be crackling? must they not be crackling?
Perfect
must I not have crackled? must you not have crackled? must he not have crackled? must we not have crackled? must you not have crackled? must they not have crackled?
V-ing perfect
must I not have been crackling? must you not have been crackling? must he not have been crackling? must we not have been crackling? must you not have been crackling? must they not have been crackling?