The Earth Is of Interest to Astronomy for Many Reasons

The earth is of interest to astronomy for many reasons. Nearly all observations must be made through the atmosphere, and the phenomena of the upper atmosphere and the magnetosphere reflect the state of interplanetary space. The earth is also the most important object of comparison for planetologists. Hannu Karttunen, et al., Fundamental Astronomy

A) Argument; conclusion: The phenomena ... state of interplanetary space.
B) Argument; conclusion: The earth is also ... for planetologists.
C) Argument; conclusion: The earth is of interest to astronomy.
D) Nonargument.
E) Argument; conclusion: Nearly all observations ... through the atmosphere.