这场火灾的罪魁祸首是一根没有熄灭的烟头。Zhè chǎng huǒzāi de zuìkuíhuòshǒu shì yī gēn méiyǒu xīmiè de yāntóu.The chief culprit of the fire was a cigarette butt that had not been put out.
医生说,长期熬夜是年轻人身体变差的罪魁祸首。Yīshēng shuō, chángqī áoyè shì niánqīngrén shēntǐ biànchà de zuìkuíhuòshǒu.The doctor said that staying up late for a long time is the main cause of young people's declining health.
别再找借口了,你自己就是这次失败的罪魁祸首。Bié zài zhǎo jièkǒu le, nǐ zìjǐ jiù shì zhè cì shībài de zuìkuíhuòshǒu.Stop making excuses — you yourself are the culprit of this failure.