it could also mean a symptom of cold when your forehead becomes hotter than usual and your body temperature rises
AKA a fever
"Temper" should be accepted here, especially given the sentence in this lesson (We suddenly lost our tempers = 우리는 갑자기 열을 냈습니다).
Still not accepted two months later (May 2021).
I wrote “ten" and it was accepted LoL