A star is located at a distance of about 100 million light years from Earth. An astronomer plans to measure the distance of the star by the parallax method. Which of these statements best explains why the astronomer's method of measuring the star distance is inappropriate?
a. At large distances, a red shift in the star's spectrum causes incorrect measurements.
b. At large distances, a blue shift in the star's spectrum causes incorrect measurements.
c. The parallaxes beyond a few thousand light years are too large to be used to measure distances.
d. The parallaxes beyond a few thousand light years are too small to be measured with common instruments.
