Susan called early this morning. She's unhappy because she's had to go to Chicago on a business trip and can't leave till tonight. She wants to be here for Grandpa.
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Sorry for posting the question here.

I think I know the rules of The Present Perfect Tense , but,this sentence is not as clear as "It has rained for 2 days." or "I 've seen the film."
P.S. I 'm not a troll. Though it 's ridiculous to ask grammar question here, I just think programmers are more smart to explain things than other people...