I could answer you could answer he could answer we could answer you could answer they could answer
V-ing form
I could be answering you could be answering he could be answering we could be answering you could be answering they could be answering
Perfect
I could have answered you could have answered he could have answered we could have answered you could have answered they could have answered
V-ing perfect
I could have been answering you could have been answering he could have been answering we could have been answering you could have been answering they could have been answering
Negation
Simple form
I couldn't answer you couldn't answer he couldn't answer we couldn't answer you couldn't answer they couldn't answer
V-ing form
I couldn't be answering you couldn't be answering he couldn't be answering we couldn't be answering you couldn't be answering they couldn't be answering
Perfect
I couldn't have answered you couldn't have answered he couldn't have answered we couldn't have answered you couldn't have answered they couldn't have answered
V-ing perfect
I couldn't have been answering you couldn't have been answering he couldn't have been answering we couldn't have been answering you couldn't have been answering they couldn't have been answering
Interrogative form
Simple form
could I answer? could you answer? could he answer? could we answer? could you answer? could they answer?
V-ing form
could I be answering? could you be answering? could he be answering? could we be answering? could you be answering? could they be answering?
Perfect
could I have answered? could you have answered? could he have answered? could we have answered? could you have answered? could they have answered?
V-ing perfect
could I have been answering? could you have been answering? could he have been answering? could we have been answering? could you have been answering? could they have been answering?
Interro-negative form
Simple form
couldn't I answer? couldn't you answer? couldn't he answer? couldn't we answer? couldn't you answer? couldn't they answer?
V-ing form
couldn't I be answering? couldn't you be answering? couldn't he be answering? couldn't we be answering? couldn't you be answering? couldn't they be answering?
Perfect
couldn't I have answered? couldn't you have answered? couldn't he have answered? couldn't we have answered? couldn't you have answered? couldn't they have answered?
V-ing perfect
couldn't I have been answering? couldn't you have been answering? couldn't he have been answering? couldn't we have been answering? couldn't you have been answering? couldn't they have been answering?