The three tenses we use in English are present, past, and future and in each tense there are four forms ( i.e. Simple, continuous, Perfect and Perfect continuous) to express the timing of action. So in all there are 12 tense forms. The for tense forms of the present tense are: Simple present, present continuous, present perfect and present perfect continuous. The present perfect is formed with are formed with the past participle form of the main verb and the helping verbs have and has,. The Present Perfect is used for a time that continues from past to present or to express completed action.
Examples: How long have you lived in Paris?
Answer: I have lived in Paris since 1990.
For more details refer to any website on English grammar. If you have any specific question, please post the same in this forum.
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