must filter
Regular verb: filter - filtered- filtered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must filter
you must filter
she must filter
we must filter
you must filter
they must filter 	I must be filtering
you must be filtering
she must be filtering
we must be filtering
you must be filtering
they must be filtering	I must have filtered
you must have filtered
she must have filtered
we must have filtered
you must have filtered
they must have filtered	I must have been filtering
you must have been filtering
she must have been filtering
we must have been filtering
you must have been filtering
they must have been filtering	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not filter
you must not filter
she must not filter
we must not filter
you must not filter
they must not filter 	I must not be filtering
you must not be filtering
she must not be filtering
we must not be filtering
you must not be filtering
they must not be filtering	I must not have filtered
you must not have filtered
she must not have filtered
we must not have filtered
you must not have filtered
they must not have filtered	I must not have been filtering
you must not have been filtering
she must not have been filtering
we must not have been filtering
you must not have been filtering
they must not have been filtering	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I filter?
must you filter?
must she filter?
must we filter?
must you filter?
must they filter? 	must I be filtering?
must you be filtering?
must she be filtering?
must we be filtering?
must you be filtering?
must they be filtering? 	must I have filtered?
must you have filtered?
must she have filtered?
must we have filtered?
must you have filtered?
must they have filtered? 	must I have been filtering?
must you have been filtering?
must she have been filtering?
must we have been filtering?
must you have been filtering?
must they have been filtering? 	

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