Astronomy professor: Stars twinkle when they are observed

5.

Astronomy professor: Stars twinkle when they are observed from Earth because of the refraction in the Earth’s atmosphere. This refraction is minor and so we don’t see any twinkling of massive objects such as the Moon and the Sun.


Student: I disagree. The Earth’s atmosphere is too transparent to cause any distortion of light coming from space. If your explanation of the twinkling of stars were correct then planets such as Mars and Venus would also twinkle when observed from Earth but they do not. I believe stars appear twinkling because they are so far away that light from them is travelling billions of miles and inevitably gets distorted by occasional aggregations of space dust.


The highlighted portions of the text perform which functions in the argument?

A: the first is the position the student disagrees with while the second is the evidence the student uses to back his opinion
B: the first is a rejection of a possible objection to the professor’s statement; the second is used as evidence in the student’s argument
C: the first is a challenge to the professor’s statement while the second mentions a fact which the student uses as evidence to refute the professor’s statement
D: the first is a consideration that casts doubt on the professor’s statement while the second is a development of this consideration
E: the first is a relevant addition to the professor’s statement while the second describes a reason why the student disagrees with this addition.