I could buzz you could buzz she could buzz we could buzz you could buzz they could buzz
V-ing form
I could be buzzing you could be buzzing she could be buzzing we could be buzzing you could be buzzing they could be buzzing
Perfect
I could have buzzed you could have buzzed she 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 she 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 she 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 she 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 she 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 she 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 she buzz? could we buzz? could you buzz? could they buzz?
V-ing form
could I be buzzing? could you be buzzing? could she be buzzing? could we be buzzing? could you be buzzing? could they be buzzing?
Perfect
could I have buzzed? could you have buzzed? could she 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 she 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 she 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 she 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 she 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 she have been buzzing? couldn't we have been buzzing? couldn't you have been buzzing? couldn't they have been buzzing?