GRE Reading Comprehension: PPO-GRE阅读PPO - M4KHI76VSWXYO83US

The appearance of the star Gamma Cephei varies regularly. The existence of a planet circling a star can cause regular variation in its appearance. However, the regular variation in Gamma Cephei's appearance is no reason to think that there is a planet circling it, since the slow rotation of a star can also cause its appearance to vary regularly and ________.