Since always refers to something which began in the past but continue suntil now, so you must use it with the present perfect tense, not the past tense.
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The use of tenses in English also is better to concise, commonly used present tense, the past tense, use less when completed, the past is finished now, tense and other composite tense basic need not.
英文摘要时态的运用也以简练为佳，常用一般现在时、一般过去时，少用现在完成时、过去完成时，进行时态和其他复合时态基本不用。
Of course not. infact, if for a minute I think that I must use the past tense, something happens to me:I freeze; I can't speak.
当然没有。如果我稍一考虑现在我得用过去时，就要出事：我僵住了，说不出话来了。
When the two actions happen at the same time, past tense is not expressed with this pattern.
当两个动作同时间发生的时候，此格式不暗示过去式。
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