Step 1: Understanding “palabra esdrújula.”
A “palabra esdrújula” is a word in which the stress falls on the antepenultimate (third-to-last) syllable, and it always carries a written accent.
Step 2: Analyze each word.
- (1) Interesante → stress on “san” (in-te-re-SAN-te); no written accent → not esdrújula.
- (2) Rápido → stress on “rá” (RÁ-pi-do); the accent mark shows stress on the third-to-last syllable → esdrújula.
- (3) Fuerte → two syllables; stress on “fuer”; not esdrújula.
- (4) Canción → stress on the last syllable (can-CIÓN); this is aguda, not esdrújula.
Step 3: Conclusion.
The only esdrújula word among the options is rápido.