I could research you could research he could research we could research you could research they could research
Forma com V-ing
I could be researching you could be researching he could be researching we could be researching you could be researching they could be researching
Perfeito
I could have researched you could have researched he could have researched we could have researched you could have researched they could have researched
Perfeito com V-ing
I could have been researching you could have been researching he could have been researching we could have been researching you could have been researching they could have been researching
Negação
Forma simple
I could not research you could not research he could not research we could not research you could not research they could not research
Forma com V-ing
I could not be researching you could not be researching he could not be researching we could not be researching you could not be researching they could not be researching
Perfeito
I could not have researched you could not have researched he could not have researched we could not have researched you could not have researched they could not have researched
Perfeito com V-ing
I could not have been researching you could not have been researching he could not have been researching we could not have been researching you could not have been researching they could not have been researching
Forma interrogativa
Forma simple
could I research? could you research? could he research? could we research? could you research? could they research?
Forma com V-ing
could I be researching? could you be researching? could he be researching? could we be researching? could you be researching? could they be researching?
Perfeito
could I have researched? could you have researched? could he have researched? could we have researched? could you have researched? could they have researched?
Perfeito com V-ing
could I have been researching? could you have been researching? could he have been researching? could we have been researching? could you have been researching? could they have been researching?
Forma interro-Negação
Forma simple
could I not research? could you not research? could he not research? could we not research? could you not research? could they not research?
Forma com V-ing
could I not be researching? could you not be researching? could he not be researching? could we not be researching? could you not be researching? could they not be researching?
Perfeito
could I not have researched? could you not have researched? could he not have researched? could we not have researched? could you not have researched? could they not have researched?
Perfeito com V-ing
could I not have been researching? could you not have been researching? could he not have been researching? could we not have been researching? could you not have been researching? could they not have been researching?