Which of the following most logically completes the argument? A. many stars that have planets circling them rotate slowly B. Gamma Cephei varies more in appearance than many other stars do C. it is easier to determine the speed at which a star rotates than to determine whether a planet is circling it D. analysis of sunspot activity on Gamma Cephei shows that it rotates slowly E. Gamma Cephei is only one of many stars that vary regularly in appearance