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