By Ray Furlong
BBC News, Berlin
Germany's authorities are holding their last major security exercise ahead of the football World Cup this summer with 2,000 people taking part in Berlin.
Germany is determined to hold a model World Cup
Three separate scenarios take place at the one time: a big screen collapse during a match, a blast at a school and a gas alert at a railway station.
The German authorities are extremely positive about hosting the World Cup, but are planning for the worst.
This week also saw an exercise dealing with hooligans rioting in Hamburg.
It is not surprising the authorities are concerned.
Officials point to the Madrid and London bombings and also the attacks on the Munich Olympics back in 1972.
Germany views the World Cup as a unique opportunity to market the country and is determined that nothing should go wrong.