concept of absolute space and time

例句：

1. 1. The concept of space travel has changed dramatically over the years.
   太空旅行的概念多年来发生了巨大变化。
2. 2. The scientist proposed a new concept for solving this problem.
   这位科学家提出了一个新的概念来解决这个难题。
3. 3. The teacher explained the concept of gravity to her students.
   老师向学生们解释了重力的概念。