I could refill you could refill he could refill we could refill you could refill they could refill
V-ing form
I could be refilling you could be refilling he could be refilling we could be refilling you could be refilling they could be refilling
Perfect
I could have refilled you could have refilled he could have refilled we could have refilled you could have refilled they could have refilled
V-ing perfect
I could have been refilling you could have been refilling he could have been refilling we could have been refilling you could have been refilling they could have been refilling
Negation
Simple form
I couldn't refill you couldn't refill he couldn't refill we couldn't refill you couldn't refill they couldn't refill
V-ing form
I couldn't be refilling you couldn't be refilling he couldn't be refilling we couldn't be refilling you couldn't be refilling they couldn't be refilling
Perfect
I couldn't have refilled you couldn't have refilled he couldn't have refilled we couldn't have refilled you couldn't have refilled they couldn't have refilled
V-ing perfect
I couldn't have been refilling you couldn't have been refilling he couldn't have been refilling we couldn't have been refilling you couldn't have been refilling they couldn't have been refilling
Interrogative form
Simple form
could I refill? could you refill? could he refill? could we refill? could you refill? could they refill?
V-ing form
could I be refilling? could you be refilling? could he be refilling? could we be refilling? could you be refilling? could they be refilling?
Perfect
could I have refilled? could you have refilled? could he have refilled? could we have refilled? could you have refilled? could they have refilled?
V-ing perfect
could I have been refilling? could you have been refilling? could he have been refilling? could we have been refilling? could you have been refilling? could they have been refilling?
Interro-negative form
Simple form
couldn't I refill? couldn't you refill? couldn't he refill? couldn't we refill? couldn't you refill? couldn't they refill?
V-ing form
couldn't I be refilling? couldn't you be refilling? couldn't he be refilling? couldn't we be refilling? couldn't you be refilling? couldn't they be refilling?
Perfect
couldn't I have refilled? couldn't you have refilled? couldn't he have refilled? couldn't we have refilled? couldn't you have refilled? couldn't they have refilled?
V-ing perfect
couldn't I have been refilling? couldn't you have been refilling? couldn't he have been refilling? couldn't we have been refilling? couldn't you have been refilling? couldn't they have been refilling?