I can straighten you can straighten he can straighten we can straighten you can straighten they can straighten
V-ing form
I can be straightening you can be straightening he can be straightening we can be straightening you can be straightening they can be straightening
Perfect
I can have straightened you can have straightened he can have straightened we can have straightened you can have straightened they can have straightened
V-ing perfect
I can have been straightening you can have been straightening he can have been straightening we can have been straightening you can have been straightening they can have been straightening
Negation
Simple form
I cannot straighten you cannot straighten he cannot straighten we cannot straighten you cannot straighten they cannot straighten
V-ing form
I cannot be straightening you cannot be straightening he cannot be straightening we cannot be straightening you cannot be straightening they cannot be straightening
Perfect
I cannot have straightened you cannot have straightened he cannot have straightened we cannot have straightened you cannot have straightened they cannot have straightened
V-ing perfect
I cannot have been straightening you cannot have been straightening he cannot have been straightening we cannot have been straightening you cannot have been straightening they cannot have been straightening
Interrogative form
Simple form
can I straighten? can you straighten? can he straighten? can we straighten? can you straighten? can they straighten?
V-ing form
can I be straightening? can you be straightening? can he be straightening? can we be straightening? can you be straightening? can they be straightening?
Perfect
can I have straightened? can you have straightened? can he have straightened? can we have straightened? can you have straightened? can they have straightened?
V-ing perfect
can I have been straightening? can you have been straightening? can he have been straightening? can we have been straightening? can you have been straightening? can they have been straightening?
Interro-negative form
Simple form
can I not straighten? can you not straighten? can he not straighten? can we not straighten? can you not straighten? can they not straighten?
V-ing form
can I not be straightening? can you not be straightening? can he not be straightening? can we not be straightening? can you not be straightening? can they not be straightening?
Perfect
can I not have straightened? can you not have straightened? can he not have straightened? can we not have straightened? can you not have straightened? can they not have straightened?
V-ing perfect
can I not have been straightening? can you not have been straightening? can he not have been straightening? can we not have been straightening? can you not have been straightening? can they not have been straightening?