Answer:
3. location
Explain:
In the sentence "Ellos están en casa hoy," the verb "estar" is used to indicate that the subject (ellos) is located at home (casa) at the time that the sentence is spoken (hoy). In Spanish, the verb "estar" is often used to indicate a temporary location, while the verb "ser" is used to indicate a more permanent or inherent characteristic. For example, you might say "Soy de España" to indicate that you are from Spain (a permanent characteristic), but you would say "Estoy en casa" to indicate that you are currently at home (a temporary location).