[讨论]求助——英语长难句——这个句子主语是什么？

gubinlaile

Hong Kong， major commercial center for Asia， and with a population which has grown at an alarming rate to over 5 million， is a city highly dependent on mass transit of all sorts， both local and long distance. The average Hong Kong worker or businessman， going about his daily activities， simply must use public transportation at one time or another.
    Because Hong Kong is in two parts， Kowloon， on the mainland side， and Hong Kong， the island， with Hong Kong‘s harbor in between， Hong Kong’s mass transit systems， in addition to going over land must also cross water.
    Going from home to work， or going shopping from one side of the harbor to the other， the Hong Kong resident has three choices. One way is to take a bus， which will cross the harbor through an underwater traffic tunnel moving slowly through bumper-to-bumper traffic. Another way is by ferryboat， a pleasant ride which crosses the harbor in from seven to fifteen minutes.
    But by far the fastest way of crossing the harbor is the newly built underground electric railway， the Hong Kong Metro. If one boards the train in the Central District， the commercial area of Hong Kong on the island side， he can speed across the harbor in an astonishing three minutes. On the other side of the harbor the railway continues， snaking back and forth through the outlying districts of Kowloon， allowing one to get off a short distance from his destination.
    The story of the Metro is an encouraging one for supporters of mass transit. Although building the system was certainly a challenging task， the Japanese firm hired to construct it did so in record time. Construction got underway in 1979 and it was completed in 1980.
For the average commuter the system has only one disadvantages： it is more expensive than by bus or ferry. One can ride the bus across the harbor for half as much， or he can ride the ferry across for less than one-fifth as much.

问题：这个句子的主语是？Because Hong Kong is in two parts， Kowloon， on the mainland side， and Hong Kong， the island， with Hong Kong‘s harbor in between， Hong Kong’s mass transit systems， in addition to going over land must also cross water.

fengyuwuzu

:funk:

lenin722

这个吗？Hong Kong’s mass transit systems