Please help me with this Spanish work

Use the right ser, or ir conjugation.

Which one of the following is the correct rhyme to keep in mind when using the spanish counterparts to this, that, those and these? a: “that” and “those” both have s’s, “this” and “these” don’t b: “that” and “those” both have t’s, “this” and “these” don’t c: “this” and “these” both have s’s, “that” and “those” don’t d: “this” and “these” both have t’s, “that” and “those” don’t

—¿ es tu celebración favorita? —mi celebración favorita es el cumpleaños de mis hijos.