Acute words are those in which the voice is accented in the last syllable. These words carry accents when they end in "n, s or vowel".
So, interest carries an accent.
"Interés"
The serious words are those in which the voice is accentuated in the penultimate syllable. Serious words have a tilde when they end in any consonant, less n or s.
So, the exam does not have an accent.
"Examen"
The words esdrujulas are those in which the voice is emphasized in the antebellum syllable. These words always carry accents.
Explanation: I took the exam and I chose the 3rd option and I got it wrong. It is not made from light material. Anyway I think it's 1st more than the 2nd. Good day!