摘要：美国联邦调查局(FBI)星期三宣布，通过初步检测，在一封邮寄给美国总统奥巴马的邮件中检测出蓖麻毒素。你知道怎么用英语表达吗?

The FBI confirmed on Wednesday a letter addressed to President Barack Obama has been preliminarily tested positive for ricin but the authorities have not found a link to Monday's Boston bombings.

The letter arrived on Tuesday, the same day that another letter addressed to a US senator was intercepted and initially tested positive for ricin, a highly toxic substance.

The incidents came one day after two explosions occurred near the finish line of the Boston Marathon, killing three people and wounding over 170 others. The authorities have called the Boston bombings an "act of terror," but the motives and perpetrators remain unknown.

美国联邦调查局(FBI)星期三宣布，通过初步检测，在一封邮寄给美国总统奥巴马的邮件中检测出蓖麻毒素。但当局并未发现这起事件与星期一的波士顿爆炸案之间的联系。这封信是星期二送达的，而在同一天，在截获的一封邮寄给美国参议员的信件中检测出了一种剧毒物质—蓖麻毒素。

这起事件发生在波士顿马拉松爆炸案一天之后，这起爆炸案造成了3人死亡，170多人受伤。当局表示波士顿爆炸案是一起恐怖袭击，但这起爆炸案的动机和疑犯依旧是个谜。

【讲解】

“ricin”解释为蓖麻毒素，最强烈天然毒素之一，如果吸入或吞服，致死剂量仅为1毫克。“Boston bombings”是指波士顿爆炸案，美国波士顿马拉松15日发生连环爆炸，共造成3人死亡，其中包括一名中国留学生，170多人受伤。