Since Venus rotates slowly, Fred Whipple thought that like Mercury, Venus keeps one face always towards the Sun. If so, he said that the dark side would be very cold. However, he knew with the help of earlier study carried out by Petit and Nicholson that it was not the case. So, he concluded that the planet must rotate fairly often to keep the darker side warmer. Which of the following is the original premiss ?

• A. Slow rotation of Venus
• B. Temperature of Venus.
• C. Frequent rotation of Venus n
• D. Equality of the rate of rotation and revolutio