must cost
Irregular verb: cost - cost- cost

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must cost
you must cost
she must cost
we must cost
you must cost
they must cost 	I must be costing
you must be costing
she must be costing
we must be costing
you must be costing
they must be costing	I must have cost
you must have cost
she must have cost
we must have cost
you must have cost
they must have cost	I must have been costing
you must have been costing
she must have been costing
we must have been costing
you must have been costing
they must have been costing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not cost
you must not cost
she must not cost
we must not cost
you must not cost
they must not cost 	I must not be costing
you must not be costing
she must not be costing
we must not be costing
you must not be costing
they must not be costing	I must not have cost
you must not have cost
she must not have cost
we must not have cost
you must not have cost
they must not have cost	I must not have been costing
you must not have been costing
she must not have been costing
we must not have been costing
you must not have been costing
they must not have been costing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I cost?
must you cost?
must she cost?
must we cost?
must you cost?
must they cost? 	must I be costing?
must you be costing?
must she be costing?
must we be costing?
must you be costing?
must they be costing? 	must I have cost?
must you have cost?
must she have cost?
must we have cost?
must you have cost?
must they have cost? 	must I have been costing?
must you have been costing?
must she have been costing?
must we have been costing?
must you have been costing?
must they have been costing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I not cost?
must you not cost?
must she not cost?
must we not cost?
must you not cost?
must they not cost? 	must I not be costing?
must you not be costing?
must she not be costing?
must we not be costing?
must you not be costing?
must they not be costing? 	must I not have cost?
must you not have cost?
must she not have cost?
must we not have cost?
must you not have cost?
must they not have cost? 	must I not have been costing?
must you not have been costing?
must she not have been costing?
must we not have been costing?
must you not have been costing?
must they not have been costing?