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