31. Based on an order-of-magnitude estimate, what is the radius of the Earth in the unit of kilometer
(km)?
Hint: The meter was originally defined in 1793 as one ten-millionth of the distance from
the equator to the North Pole along a great circle.
(A) 2
(B) 4
(C) 6
(D) 8
(E) 10
阿摩線上測驗
登入