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