Welcome to EF, Zhuk There is no unanimous "correct" reply to your last question. As a rule, English is very flexible and in many cases liberal grammarians accept more than one alternative while some others insist on only one that they think is right. I would go for has , like you.
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AnonymousCan you please tell what works best for you when you check grammar?I have no special method. I just read what I have written and hopefully anything totally wrong will jar in my ear pretty much the same way a wrong note in music does. If I am writing something really serious, I analyze my language thoughtfully word for word.