Final answer:
The reason why ser is used in the sentence "Hoy es el 1 de octubre de 2019" is because it is indicating the time/date. Ser is used to express the date, day, and time.
Step-by-step explanation:
The reason why ser is used in the sentence "Hoy es el 1 de octubre de 2019" is because it is indicating the time/date on which the sentence is referring to. Ser is used to express the date, day, and time. In this case, it is stating that "Today is the 1st of October 2019".
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