Что такое подлежащее (Subject)?

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Подлежащее (субъект) — тот, кто (who) или что (what) выполняет действие.
*I* am hungry
My *brother* is very smart
That *computer* is very expensive"
*We* are going to the store now
My *sister and I* will be waiting here"
*The building* is very big
When are *you* going to eat lunch?"
"Why are *they* waiting in line?"
*Who* is going to take you to the ballet show?