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