Complex sentence: Colas Group is a major French civil engineering firm specialising in road construction, and also rail track construction through the subsidiary Colas Rail, since the 1990s the group has incorporated the road construction firms Screg and Sacer.
Split into simpler sentences: Colas Group is a major French civil engineering firm specialising in road construction and rail track construction through its subsidiary Colas Rail. Since the 1990s the group has incorporated the road construction firms Screg and Sacer.