Which of the following statements is true? a. a 140-lb. person would weigh more than 140 lbs on the moon because of the increase in gravity. b. earth has a synchronous rotation, when means its rotation and revolution periods are the same length. c. earth's moon is unique because it is larger than any other natural satellite in the solar system. d. leap years add an extra day to february because the earth takes longer than 365 days to orbit the sun.