I must underestimate you must underestimate she must underestimate we must underestimate you must underestimate they must underestimate
V-ing form
I must be underestimating you must be underestimating she must be underestimating we must be underestimating you must be underestimating they must be underestimating
Perfect
I must have underestimated you must have underestimated she must have underestimated we must have underestimated you must have underestimated they must have underestimated
V-ing perfect
I must have been underestimating you must have been underestimating she must have been underestimating we must have been underestimating you must have been underestimating they must have been underestimating
Negation
Simple form
I mustn't underestimate you mustn't underestimate she mustn't underestimate we mustn't underestimate you mustn't underestimate they mustn't underestimate
V-ing form
I mustn't be underestimating you mustn't be underestimating she mustn't be underestimating we mustn't be underestimating you mustn't be underestimating they mustn't be underestimating
Perfect
I mustn't have underestimated you mustn't have underestimated she mustn't have underestimated we mustn't have underestimated you mustn't have underestimated they mustn't have underestimated
V-ing perfect
I mustn't have been underestimating you mustn't have been underestimating she mustn't have been underestimating we mustn't have been underestimating you mustn't have been underestimating they mustn't have been underestimating
Interrogative form
Simple form
must I underestimate? must you underestimate? must she underestimate? must we underestimate? must you underestimate? must they underestimate?
V-ing form
must I be underestimating? must you be underestimating? must she be underestimating? must we be underestimating? must you be underestimating? must they be underestimating?
Perfect
must I have underestimated? must you have underestimated? must she have underestimated? must we have underestimated? must you have underestimated? must they have underestimated?
V-ing perfect
must I have been underestimating? must you have been underestimating? must she have been underestimating? must we have been underestimating? must you have been underestimating? must they have been underestimating?
Interro-negative form
Simple form
mustn't I underestimate? mustn't you underestimate? mustn't she underestimate? mustn't we underestimate? mustn't you underestimate? mustn't they underestimate?
V-ing form
mustn't I be underestimating? mustn't you be underestimating? mustn't she be underestimating? mustn't we be underestimating? mustn't you be underestimating? mustn't they be underestimating?
Perfect
mustn't I have underestimated? mustn't you have underestimated? mustn't she have underestimated? mustn't we have underestimated? mustn't you have underestimated? mustn't they have underestimated?
V-ing perfect
mustn't I have been underestimating? mustn't you have been underestimating? mustn't she have been underestimating? mustn't we have been underestimating? mustn't you have been underestimating? mustn't they have been underestimating?