Mary made a mark in the textbook, where the meaning of the sentence is unclear.

玛丽在课本上句子意思不清楚的地方做了一个记号。

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Despite commonly held beliefs, it's unclear whether the Columbine shooters timed that attack to mark either Adolf Hitler's birthday or the Waco incident.

CNN: Boston Marathon bombing: The latest Patriots Day tragedy

Mark Foxall from the authority said it was unclear if the damage was accidental or not.

BBC: Shrewsbury Cemetery graves extensively damaged

That's an improvement from the 13- to 14, 000 customers who were without electricity at one point, but it's unclear when power would be restored to everyone, spokesman Mark Davis said.

CNN: Tornado tears through southern Mississippi