I could frost you could frost he could frost we could frost you could frost they could frost
V-ing form
I could be frosting you could be frosting he could be frosting we could be frosting you could be frosting they could be frosting
Perfect
I could have frosted you could have frosted he 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 he 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 he 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 he 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 he 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 he 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 he frost? could we frost? could you frost? could they frost?
V-ing form
could I be frosting? could you be frosting? could he be frosting? could we be frosting? could you be frosting? could they be frosting?
Perfect
could I have frosted? could you have frosted? could he 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 he 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 he 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 he 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 he 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 he have been frosting? couldn't we have been frosting? couldn't you have been frosting? couldn't they have been frosting?