New words：

twister ['twistər] n.旋风；龙卷风；难题
brain twister 脑筋急转弯；智力难题

Sample Sentences：

That's a real twister.
The girl is very good at the brain twister game.
The National Weather Service says at least 50 twisters were reported.
Pick three to five tongue twisters every day and practice them a few times.

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