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