must investigate
Regular verb: investigate - investigated- investigated

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must investigate
you must investigate
she must investigate
we must investigate
you must investigate
they must investigate 	I must be investigating
you must be investigating
she must be investigating
we must be investigating
you must be investigating
they must be investigating	I must have investigated
you must have investigated
she must have investigated
we must have investigated
you must have investigated
they must have investigated	I must have been investigating
you must have been investigating
she must have been investigating
we must have been investigating
you must have been investigating
they must have been investigating	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must not investigate
you must not investigate
she must not investigate
we must not investigate
you must not investigate
they must not investigate 	I must not be investigating
you must not be investigating
she must not be investigating
we must not be investigating
you must not be investigating
they must not be investigating	I must not have investigated
you must not have investigated
she must not have investigated
we must not have investigated
you must not have investigated
they must not have investigated	I must not have been investigating
you must not have been investigating
she must not have been investigating
we must not have been investigating
you must not have been investigating
they must not have been investigating	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I investigate?
must you investigate?
must she investigate?
must we investigate?
must you investigate?
must they investigate? 	must I be investigating?
must you be investigating?
must she be investigating?
must we be investigating?
must you be investigating?
must they be investigating? 	must I have investigated?
must you have investigated?
must she have investigated?
must we have investigated?
must you have investigated?
must they have investigated? 	must I have been investigating?
must you have been investigating?
must she have been investigating?
must we have been investigating?
must you have been investigating?
must they have been investigating? 	

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