This generation of soldiers, sailors, airmen, Marines and Coast Guardsmen have volunteered in the time of certain danger.

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Mr. Calleja believes that modern opera productions also have to be believable, and said that he can recognize certain danger signals while rehearsing a new production.

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Worse, Mr Thurlow says that Mr Kerry's boat fled from the scene after the mine exploded, turning back to go to the aid of the disabled boat only when its captain was certain there was no danger.

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For animals, certain sounds, such as growling, mean danger.

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It is inconsistent, they say, for governments that do not allow young people to vote, buy alcohol, drive, marry without their parents' consent or accept certain kinds of civilian employment to send them into mortal danger instead.

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