must stiffen
Verbo regular: stiffen - stiffened- stiffened

Afirmação 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
I must stiffen
you must stiffen
she must stiffen
we must stiffen
you must stiffen
they must stiffen 	I must be stiffening
you must be stiffening
she must be stiffening
we must be stiffening
you must be stiffening
they must be stiffening	I must have stiffened
you must have stiffened
she must have stiffened
we must have stiffened
you must have stiffened
they must have stiffened	I must have been stiffening
you must have been stiffening
she must have been stiffening
we must have been stiffening
you must have been stiffening
they must have been stiffening	

Negação 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
I must not stiffen
you must not stiffen
she must not stiffen
we must not stiffen
you must not stiffen
they must not stiffen 	I must not be stiffening
you must not be stiffening
she must not be stiffening
we must not be stiffening
you must not be stiffening
they must not be stiffening	I must not have stiffened
you must not have stiffened
she must not have stiffened
we must not have stiffened
you must not have stiffened
they must not have stiffened	I must not have been stiffening
you must not have been stiffening
she must not have been stiffening
we must not have been stiffening
you must not have been stiffening
they must not have been stiffening	

Forma interrogativa 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
must I stiffen?
must you stiffen?
must she stiffen?
must we stiffen?
must you stiffen?
must they stiffen? 	must I be stiffening?
must you be stiffening?
must she be stiffening?
must we be stiffening?
must you be stiffening?
must they be stiffening? 	must I have stiffened?
must you have stiffened?
must she have stiffened?
must we have stiffened?
must you have stiffened?
must they have stiffened? 	must I have been stiffening?
must you have been stiffening?
must she have been stiffening?
must we have been stiffening?
must you have been stiffening?
must they have been stiffening? 	

Forma interro-Negação 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
must I not stiffen?
must you not stiffen?
must she not stiffen?
must we not stiffen?
must you not stiffen?
must they not stiffen? 	must I not be stiffening?
must you not be stiffening?
must she not be stiffening?
must we not be stiffening?
must you not be stiffening?
must they not be stiffening? 	must I not have stiffened?
must you not have stiffened?
must she not have stiffened?
must we not have stiffened?
must you not have stiffened?
must they not have stiffened? 	must I not have been stiffening?
must you not have been stiffening?
must she not have been stiffening?
must we not have been stiffening?
must you not have been stiffening?
must they not have been stiffening?