The time period is 'up to now' - a time period that we typically associate with the present perfect.
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norwolfPersonally, I can't really agree that "we typically associate with the present perfect",Fine, though I don't really see why you ask questions here if you feel you know the answers better than those teachers who respond.
norwolfwhich is a one-side conclusion.Interesting idea.
norwolfIn other
fivejedjonwhy you ask questions here if you feel you know the answers better than those teachers who respond.Oh,so sorry, dear fivejedjon. Did I make any mistake? Actually, i just suspected the given answer, and wished you teachers would have shared your excellent views with me.