Complete the sentence: I _______ him since 2005.

The correct answer is "have known". Explanation: The sentence requires the present perfect tense because it describes an action (knowing someone) that started in the past (2005) and continues to the present. The present perfect tense is formed with "have/has + past participle". * "have known" is the correct form for the subject "I". * "has known" is used with singular subjects like "he", "she", or "it". * "have knew" is grammatically incorrect because "knew" is the past simple form, and the past participle of "know" is "known". * "knew" is the past simple form, which doesn't fit the "since 2005" time frame implying a continuing action. Therefore, the correct sentence is: I have known him since 2005.