The pre-warning effect not just depends on the quality of forecast method and the warning limit, but relies on whether there is a reasonable pre-warning index system.

预警效果的好坏不仅依赖预测方法的优劣和警界限的准确与否，而且依赖于是否有一个合理的预警指标体系。

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Apple tells its customers they must not download an app if they fall below the stated age limit - but users can click away the warning message.

BBC: Twitter's Vine app gets adult rating on Apple store

We filmed 15 vehicles including a bus, a post van and numerous cars which, according to a flashing speed warning sign, were breaking the limit.

BBC: Will a borough-wide 20mph speed limit work?

The conviction of a trawlerman illegally fishing within Guernsey's 12-mile limit will act as a warning to others, according to the States.

BBC: Brixham registered beam trawler in St Peter Port Harbour