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.
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。
Scientists believe that Mercury's core — an immense iron body that accounts for roughly 75 percent of the entire planet's mass — has helped the planet to win the density prize.
科学家认为,水星的核心- -一个巨大的铁体,大约占整个行星的75%——帮助这个星球赢得密度奖。
Optimists in the Enlightenment and the 19th century came to believe that the mass of humanity could one day lead happy and worthy lives here on Earth.
18世纪启蒙运动和19世纪中的乐观主义者相信在全人类总有一天能够在地球上过上幸福和有价值的生活。
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