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