Complex sentence: The GPDA was reformed over the weekend of the 1994 Monaco Grand Prix, following the deaths of Ayrton Senna and Roland Ratzenberger, as well as the serious accident of Rubens Barrichello at the San Marino Grand Prix two weeks before.
Split into simpler sentences: The GPDA was reformed over the weekend of the 1994 Monaco Grand Prix. This followed the deaths of Ayrton Senna and Roland Ratzenberger, as well as the serious accident of Rubens Barrichello at the San Marino Grand Prix two weeks before.