Question

reading & writing - part 1
while researching a topic, a student has taken the following notes:

• polaris, also called the north star, holds the same position in the sky of the northern hemisphere year - round.
• polaris is a cepheid star, meaning that it swells regularly in brightness and size.
• the stellar evolution model, which typically produces highly accurate readings of cepheid stars, concludes that polaris has a mass seven times that of our sun.
• another approach, combining images from telescopes and data about polaris orbit, concludes that polaris has a mass 3.5 that of our sun.

the student wants to explain why the stellar evolution model has been used to measure polaris mass. which choice most effectively uses relevant information from the notes to accomplish this goal?
a because the stellar evolution model usually yields accurate information about cepheid stars, it is one of the approaches scientists have taken to determine the mass of the cepheid polaris.
b despite generally being an accurate source of data about cepheid stars, the stellar evolution model produces different results than a study of polaris appearance and orbit.
c it is ironic that, despite polaris holding a stable position in the sky, studies of its mass do not produce stable results.
d because the stellar evolution model is typically accurate when analyzing cepheid stars, it is likely that polaris mass is in fact seven times greater than that of our sun.

Explanation:

The goal is to explain why the stellar - evolution model has been used to measure Polaris' mass. Option A directly states that since the model usually gives accurate information about cepheid stars (and Polaris is a cepheid star), it is one of the approaches to determine Polaris' mass. Option B focuses on the difference between the model and another approach rather than why the model is used. Option C is about the irony of mass - study results and not about the use of the model. Option D makes a claim about the actual mass value rather than why the model is used.

Answer:

A. Because the stellar evolution model usually yields accurate information about cepheid stars, it is one of the approaches scientists have taken to determine the mass of the cepheid Polaris