I could supplement you could supplement she could supplement we could supplement you could supplement they could supplement
V-ing form
I could be supplementing you could be supplementing she could be supplementing we could be supplementing you could be supplementing they could be supplementing
Perfect
I could have supplemented you could have supplemented she could have supplemented we could have supplemented you could have supplemented they could have supplemented
V-ing perfect
I could have been supplementing you could have been supplementing she could have been supplementing we could have been supplementing you could have been supplementing they could have been supplementing
Negation
Simple form
I couldn't supplement you couldn't supplement she couldn't supplement we couldn't supplement you couldn't supplement they couldn't supplement
V-ing form
I couldn't be supplementing you couldn't be supplementing she couldn't be supplementing we couldn't be supplementing you couldn't be supplementing they couldn't be supplementing
Perfect
I couldn't have supplemented you couldn't have supplemented she couldn't have supplemented we couldn't have supplemented you couldn't have supplemented they couldn't have supplemented
V-ing perfect
I couldn't have been supplementing you couldn't have been supplementing she couldn't have been supplementing we couldn't have been supplementing you couldn't have been supplementing they couldn't have been supplementing
Interrogative form
Simple form
could I supplement? could you supplement? could she supplement? could we supplement? could you supplement? could they supplement?
V-ing form
could I be supplementing? could you be supplementing? could she be supplementing? could we be supplementing? could you be supplementing? could they be supplementing?
Perfect
could I have supplemented? could you have supplemented? could she have supplemented? could we have supplemented? could you have supplemented? could they have supplemented?
V-ing perfect
could I have been supplementing? could you have been supplementing? could she have been supplementing? could we have been supplementing? could you have been supplementing? could they have been supplementing?
Interro-negative form
Simple form
couldn't I supplement? couldn't you supplement? couldn't she supplement? couldn't we supplement? couldn't you supplement? couldn't they supplement?
V-ing form
couldn't I be supplementing? couldn't you be supplementing? couldn't she be supplementing? couldn't we be supplementing? couldn't you be supplementing? couldn't they be supplementing?
Perfect
couldn't I have supplemented? couldn't you have supplemented? couldn't she have supplemented? couldn't we have supplemented? couldn't you have supplemented? couldn't they have supplemented?
V-ing perfect
couldn't I have been supplementing? couldn't you have been supplementing? couldn't she have been supplementing? couldn't we have been supplementing? couldn't you have been supplementing? couldn't they have been supplementing?