I can refer you can refer she can refer we can refer you can refer they can refer
V-ing form
I can be referring you can be referring she can be referring we can be referring you can be referring they can be referring
Perfect
I can have referred you can have referred she can have referred we can have referred you can have referred they can have referred
V-ing perfect
I can have been referring you can have been referring she can have been referring we can have been referring you can have been referring they can have been referring
Negation
Simple form
I cannot refer you cannot refer she cannot refer we cannot refer you cannot refer they cannot refer
V-ing form
I cannot be referring you cannot be referring she cannot be referring we cannot be referring you cannot be referring they cannot be referring
Perfect
I cannot have referred you cannot have referred she cannot have referred we cannot have referred you cannot have referred they cannot have referred
V-ing perfect
I cannot have been referring you cannot have been referring she cannot have been referring we cannot have been referring you cannot have been referring they cannot have been referring
Interrogative form
Simple form
can I refer? can you refer? can she refer? can we refer? can you refer? can they refer?
V-ing form
can I be referring? can you be referring? can she be referring? can we be referring? can you be referring? can they be referring?
Perfect
can I have referred? can you have referred? can she have referred? can we have referred? can you have referred? can they have referred?
V-ing perfect
can I have been referring? can you have been referring? can she have been referring? can we have been referring? can you have been referring? can they have been referring?
Interro-negative form
Simple form
can I not refer? can you not refer? can she not refer? can we not refer? can you not refer? can they not refer?
V-ing form
can I not be referring? can you not be referring? can she not be referring? can we not be referring? can you not be referring? can they not be referring?
Perfect
can I not have referred? can you not have referred? can she not have referred? can we not have referred? can you not have referred? can they not have referred?
V-ing perfect
can I not have been referring? can you not have been referring? can she not have been referring? can we not have been referring? can you not have been referring? can they not have been referring?