单选题 To prevent a repetition of this dreadful occurrence, we must discover the element in the food that was served.

【正确答案】 B
【答案解析】(toxic有毒的)。句意为：为了防止这种可怕的事件再度发生，我们一定要找出端上来的食品中有毒的成分。A．unknown未知的；C．kind仁慈的；D．shameful可耻的。