Scientists have known for a long time that aerosols such as soot, dust and other small particulate matter, alter cloud density and the radiative balance of the atmosphere.
科学家们很早之前就发现，诸如煤烟、灰尘和其他细小的微粒，能改变云体的密度及大气的辐射平衡。
2
As we get older, we lose lean muscle mass, bone density, balance and flexibility-all of which can make it harder to move around.
当我们逐渐衰老是，我们会丧失一些肌肉组织，骨骼密度、平衡能力和灵活性，这些都将使我们行动力减退。
3
Total bone mineral density, balance, and flexibility did not improve significantly in either group.