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