About 50 passengers were burned to  death(死亡) on BRT in Xiamen on June 7th,2013.这道题空里为什么要填death?

About 50 passengers were burned to  death(死亡) on BRT in Xiamen on June 7th,2013.这道题空里为什么要填death?
About 50 passengers were burned to  death(死亡) on BRT in Xiamen on June 7th,2013.
这道题空里为什么要填death?

About 50 passengers were burned to  death(死亡) on BRT in Xiamen on June 7th,2013.这道题空里为什么要填death?
burned to death 被烧死
这是习语,英语就是这样说的.
动词的分词形式 + to death 是固定搭配.
其他类似短语：
He was beaten to death 他被打死
I was bored to death 我很无聊到死
The bandits shot him to death 土匪开枪将他打死