大多数天文学家认为，星系中心的大量物质是一个黑洞，它的引力导致气体旋转。
Most astronomers believe that the large concentration of mass at the galaxy's center is a black hole whose gravity is causing the gas to whirl.
接待家庭主要在第2区和第3区，大多数接待家庭并不住在第1区，因为纽约市中心的大部分地方都是贸易中心。
Host families are mainly in Zones 2, 3 and most hosts don't live in Zone 1 because much of central New York is trading center.
墨尔本庞大的轨道电车网络大大降低了私家车在市中心的使用率，但是远郊地区却与其他大多数的澳大利亚城市一样，有着同样的基于私家车的交通结构。
Melbourne's large tram network has made car use in the inner city much lower, but the outer suburbs have the same car-based structure as most other Australian cities.
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