"nobil"> Just like people, stars also have lifespan. A star keeps the same color and shape for most of its life. But when it gets very old, it swells into what is called a red giant. After reaching this stage, some stars begin to cool down and grow dim. Other stars explode into spectacular supernovas. 就像人类一样，星星也有平均寿命。星星的一生大多数会维持相同的颜色与形状，但是当时间一久，就会膨胀变成红色的巨星，这时，有些星星的温度会开始下降，光度也随之下降。有些星星会爆炸，形成壮观的超新星。 编辑推荐：名师指导公共英语阅读考试技巧 公共英语pets三级全真模拟试卷 公共英语pets二级语法讲解汇总