must crumble
Verbo regular: crumble - crumbled- crumbled

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I must crumble
you must crumble
he must crumble
we must crumble
you must crumble
they must crumble 	I must be crumbling
you must be crumbling
he must be crumbling
we must be crumbling
you must be crumbling
they must be crumbling	I must have crumbled
you must have crumbled
he must have crumbled
we must have crumbled
you must have crumbled
they must have crumbled	I must have been crumbling
you must have been crumbling
he must have been crumbling
we must have been crumbling
you must have been crumbling
they must have been crumbling	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I must not crumble
you must not crumble
he must not crumble
we must not crumble
you must not crumble
they must not crumble 	I must not be crumbling
you must not be crumbling
he must not be crumbling
we must not be crumbling
you must not be crumbling
they must not be crumbling	I must not have crumbled
you must not have crumbled
he must not have crumbled
we must not have crumbled
you must not have crumbled
they must not have crumbled	I must not have been crumbling
you must not have been crumbling
he must not have been crumbling
we must not have been crumbling
you must not have been crumbling
they must not have been crumbling	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
must I crumble?
must you crumble?
must he crumble?
must we crumble?
must you crumble?
must they crumble? 	must I be crumbling?
must you be crumbling?
must he be crumbling?
must we be crumbling?
must you be crumbling?
must they be crumbling? 	must I have crumbled?
must you have crumbled?
must he have crumbled?
must we have crumbled?
must you have crumbled?
must they have crumbled? 	must I have been crumbling?
must you have been crumbling?
must he have been crumbling?
must we have been crumbling?
must you have been crumbling?
must they have been crumbling? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
must I not crumble?
must you not crumble?
must he not crumble?
must we not crumble?
must you not crumble?
must they not crumble? 	must I not be crumbling?
must you not be crumbling?
must he not be crumbling?
must we not be crumbling?
must you not be crumbling?
must they not be crumbling? 	must I not have crumbled?
must you not have crumbled?
must he not have crumbled?
must we not have crumbled?
must you not have crumbled?
must they not have crumbled? 	must I not have been crumbling?
must you not have been crumbling?
must he not have been crumbling?
must we not have been crumbling?
must you not have been crumbling?
must they not have been crumbling?