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The verb ‘Do’ can function as a main verb as well as an auxiliary verb (also called helping verb) like can, have, is, and will. As helping verb it is primarily used to form negative or interrogative sentence in simple present or past tense, with a main verb; as: § Negative sentence: I do not play football. (simple present) She does not know English. You did not come to my house yesterday. (simple past) § Interrogative sentence (questions) Do I play football? Does she know English? How do you do? Did you come to my house yesterday?