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