The answer, in my opinion, is the second sentence, "The coach who is an expert in the sport explained the revised rules to us". Here, the "Who is an expert", is presumably the nonessential clause.
Explanation:
B ) thoughts feelings and insights about an event
Italian name: Colosseo
The Roman Colosseum or Coliseum, originally known as the Flavian Amphitheatre, was commisioned in AD 72 by Emperor Vespasian. It was completed by his son, Titus, in 80, with later improvements by Domitian.
The Colosseum is located just east of the Roman Forum and was built to a practical design, with its 80 arched entrances allowing easy access to 55,000 spectators, who were seated according to rank. The Coliseum is huge, an ellipse 188m long and 156 wide. Originally 240 masts were attached to stone corbels on the 4th level.
Just outside the Coliseum is theArch of Constantine (Arco di Costantino), a 25m high monument built in AD315 to mark the victory of Constantine over Maxentius at Pons Milvius.
Vespesian ordered the Colosseum to be build on the site of Nero's palace, the Domus Aurea, to dissociate himself from the hated tyrant.
His aim was to gain popularity by staging deadly combats of gladiators and wild animal fights for public viewing. Massacre was on a huge scale: at inaugural games in AD 80, over 9,000 wild animals were killed.
