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