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