I don't understand the example, but I think what they are trying to get to is that the base or infinitive form is normally the same as the simple present 1st person form: go - to go - I go see - to see - I see extinguish - to extinguish - I extinguish But with 'be', it is not: be - to be - I am Be' doesn't really have a base form in the same sense as other verbs, since it is not the base for any of the common finite forms ( am, is, are, was, were )
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