Everyone answered the question correctly, but then I’d love to explain it another way just to help.
(1) Ser is used to describe a topic or a subject with its natural traits or, permanent traits.
E.g. El sol es caliente.
(The sun is hot. - The sun is naturally hot, and the likelihood of it getting cold is inexistent.)
(Although it is also valid to say “El sol está caliente”, but implying the nuance of heat as a temporal physical state (that the sun will eventually cool down.))
La edificio en la calle 18´ es alto. (The building along 18th street is tall.) (A natural, permanent, unlikely to change trait.)
(2) In lieu of #1, Ser also then is used to explain a person’s non-temporal qualities.
Mercedes es muy linda. (Mercedes is very pretty.) Pretty being a natural trait, albeit temporal, it is not likely to change quickly.
Los estudiantes son muy inteligentes. (The students are very intelligent.)
(3) Also in lieu of #1, it also is used to indicate a persons nationality, race, creed, gender, and such, as these do not simply change over time, (or its likelihood to change is slim).
El Señor Aldama es Filipino. (Mr Aldama is Filipino.)
Mis padres son Católicos, pero yo soy un Cristiano regular. (My parents are Catholics, I however am a regular Christian.)
La persona [que está en la oficina] es mujer. (The person in the office is a woman.) (Also note that in this case, the subject is associated with another noun and not an adjective. Which leads to the fourth item.
(4) Ser is used to associate nouns to other nouns e.g.
Mis hermanos son doctores. (My brothers are doctors.) (Hermanos, and Doctores, are nouns associated with each other to form a description.)
(5) As basic as it is, Ser is used to express time. E.g.
Es la una. Son las tres y media. Son las cinco y cuarenta y cinco de la tarde. (1:00, 3:30, 5:45pm etc.)
Lourdes A.
04/05/20