Complex sentence: The third session on Saturday morning saw Vettel fastest, ahead of Alonso, Rosberg and Massa, with a KERS failure on Mark Webber's RB7 preventing him from participating.
Split into simpler sentences: The third session on Saturday morning saw Vettel fastest, ahead of Alonso, Rosberg and Massa. A KERS failure on Mark Webber's RB7 prevented him from participating.