Question

read the source of the allusion.
kryptonite, matter from supermans home planet, is the only thing that can reduce the superheros strength.
what is the meaning of the allusion in the sentence below?
sappy love songs are kryptonite to my otherwise stoic father.
a source of weakness
a source of displeasure

Explanation:

The source says Kryptonite reduces Superman's strength (a weakness for him). In the sentence, sappy love songs are Kryptonite to a stoic father—stoic means emotionally strong, so the songs would be a source of weakness (undermining his stoic nature), not just displeasure. So the first option fits.

Answer:

a source of weakness