下降，落下to fall

• 月亮已经沉落下去。

  The moon has already disappeared.

• “金钩”般的太阳缓缓沉落地平线。

  The sun, looking like a golden hook, slowly sets over the horizon.

• 在一次大地震中,整座城沉落海底。

  During a major earthquake, the whole city sinks to the seabed.

• 心绪沉落

  feel depressed