Answer:
G. The star is cooler than a blue star
Step-by-step explanation:
If the star the astronomer observed is similar in color and size to our sun, then it's impossible for it to be a white dwarf star because they are white and much smaller, while the star the astronomer observed had to have been some shade of yellow or orange and is similar in size to our sun.
A blue star is hotter than our sun by approximately 5000 kelvin. If the star observed is similar in color to our sun then we know that it hasn't reached a temperature hot enough to surpass a blue star, for colors of star change depending on temperature.
Our sun is not as bright as a red giant star. If the observed star was similar in color and size to the sun, then it couldn't have been as bright either.
There is no evidence that supports the star is farther away from other stars in the solar system.
Therefore, the option that makes the most sense is option G.
hope this helps :)