Without gravity, astronauts' bones and muscles weaken over time.

没有重力，宇航员的骨骼和肌肉会随时间减弱。

同一单元的其他句子

• Space exploration has inspired many young people to pursue careers in science.太空探索激励了许多年轻人从事科学事业。
• The astronauts conducted experiments on the International Space Station.宇航员在国际空间站上进行了实验。
• Can humans survive on Mars in the future?人类将来能在火星上生存吗？
• Do not underestimate the challenges of long-duration spaceflight.不要低估长期太空飞行的挑战。
• The telescope discovered a new exoplanet orbiting a distant star.望远镜发现了一颗围绕遥远恒星运行的新系外行星。