The London underground is the oldest system, having opened in 1863. It is also the largest system, with 394 kilometres of route.
The Los Angeles network is the newest, having opened in 2001, while the Kyoto network is the smallest and serves only 45 million passengers per year.
这个句子是出自,雅思考官simon范文里的。
请问having opened这里是什么时态,这样写对吗?