The Arabic expression كالنار في الهشيم (ka-l-nār fī al-hashīm) is an idiomatic phrase that literally translates to "like fire in dry brush." The word الهشيم refers to dry, brittle plant matter or kindling that catches fire instantly. When fire meets such material, it spreads rapidly and uncontrollably. The idiom is therefore used to describe something that spreads with great speed, much like the English expression "like wildfire."
The correct meaning is تنتشر بسرعة (it spreads quickly), because the entire purpose of this simile is to convey the idea of rapid, unstoppable spread. It is commonly used to describe how news, rumours, or ideas travel through a community at remarkable speed.
The other options do not capture the core meaning of the idiom. ببطء (slowly) is the opposite of what the expression conveys. لا تؤثر (has no effect) contradicts the image of a powerful, spreading fire. محرقة (burning/destructive) focuses only on the literal fire element and misses the figurative point about speed of spread, which is the real lesson of this تعبير اصطلاحي (idiomatic expression).
