The discovery of stars orbiting the supermassive black hole at the galactic center was a turning point in astrophysics.

有时最简单的问题会引出最深奥的理论。

随机评估可以帮助我们了解发展中哪些措施有效，哪些无效。

The hardest part was letting go, not taking part.

教育儿童，就不需要惩罚成年人。