I must strengthen you must strengthen she must strengthen we must strengthen you must strengthen they must strengthen
V-ing form
I must be strengthening you must be strengthening she must be strengthening we must be strengthening you must be strengthening they must be strengthening
Perfect
I must have strengthened you must have strengthened she must have strengthened we must have strengthened you must have strengthened they must have strengthened
V-ing perfect
I must have been strengthening you must have been strengthening she must have been strengthening we must have been strengthening you must have been strengthening they must have been strengthening
Negation
Simple form
I must not strengthen you must not strengthen she must not strengthen we must not strengthen you must not strengthen they must not strengthen
V-ing form
I must not be strengthening you must not be strengthening she must not be strengthening we must not be strengthening you must not be strengthening they must not be strengthening
Perfect
I must not have strengthened you must not have strengthened she must not have strengthened we must not have strengthened you must not have strengthened they must not have strengthened
V-ing perfect
I must not have been strengthening you must not have been strengthening she must not have been strengthening we must not have been strengthening you must not have been strengthening they must not have been strengthening
Interrogative form
Simple form
must I strengthen? must you strengthen? must she strengthen? must we strengthen? must you strengthen? must they strengthen?
V-ing form
must I be strengthening? must you be strengthening? must she be strengthening? must we be strengthening? must you be strengthening? must they be strengthening?
Perfect
must I have strengthened? must you have strengthened? must she have strengthened? must we have strengthened? must you have strengthened? must they have strengthened?
V-ing perfect
must I have been strengthening? must you have been strengthening? must she have been strengthening? must we have been strengthening? must you have been strengthening? must they have been strengthening?
Interro-negative form
Simple form
must I not strengthen? must you not strengthen? must she not strengthen? must we not strengthen? must you not strengthen? must they not strengthen?
V-ing form
must I not be strengthening? must you not be strengthening? must she not be strengthening? must we not be strengthening? must you not be strengthening? must they not be strengthening?
Perfect
must I not have strengthened? must you not have strengthened? must she not have strengthened? must we not have strengthened? must you not have strengthened? must they not have strengthened?
V-ing perfect
must I not have been strengthening? must you not have been strengthening? must she not have been strengthening? must we not have been strengthening? must you not have been strengthening? must they not have been strengthening?