19. There is an interesting experiment that enables us to estimate the mass density of the sun. Consider(see Figure 5) an experimental setup that can get an image of the sun through a pinhole. The distancebetween the pinhole and the screen is d, and the diameter of the image is D. Because light propagatesin a straight line (neglect geometrical distortions), you can obtain the angle θin terms of d and D.Therefore, the relationship between R and r can be exhibited, where R is the radius of the sun and ris the distance between the earth and the sun. It is known that the earth orbits the sun by the period

days. Assume that the earth makes a circular orbit around the sun, and the sun is a perfectsphere. From these hints, the mass density of the sun p is given by
  

(A)

(B)

(C)

(D)

, where G=

is the gravitational constant.