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