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