pre-galactic cloud

例句：

1. 1.The formation of these clouds is a mystery that has puzzled scientists for decades.
   这些云的形成是科学家困惑了几十年的谜题。
2. 2.The pre-galactic cloud is believed to be the birthplace of our solar system.
   前银河云被认为是我们太阳系的起源地。
3. 3.The study of these clouds helps us understand the early history of the universe.
   研究这些云有助于我们理解宇宙的早期历史。