Sentence Correction

Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close.

A) Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close.
B) Though Saturn's main rings may appear smooth and continuous when viewed from a distance, they are in fact composed of thousands of separate icy ringlets when viewed up close.
C) Saturn's main rings, when viewed from a distance, may appear to be smooth and continuous, though when viewed up close they are in fact composed of thousands of separate icy ringlets.
D) When viewed from a distance, Saturn's main rings may appear smooth and continuous, but closer viewing reveals them to be composed of thousands of separate icy ringlets.
E) Though composed of thousands of separate icy ringlets if viewed up close, the main rings of Saturn may appear smooth and continuous when they are viewed from a distance.


OA is D

IMO D
But is required to show Contrast. Though = Even though = Although Do not should contrast they mean Despite the fact.

DhruvXVII wrote:Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close.

A) Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close.
B) Though Saturn's main rings may appear smooth and continuous when viewed from a distance, they are in fact composed of thousands of separate icy ringlets when viewed up close.
C) Saturn's main rings, when viewed from a distance, may appear to be smooth and continuous, though when viewed up close they are in fact composed of thousands of separate icy ringlets.
D) When viewed from a distance, Saturn's main rings may appear smooth and continuous, but closer viewing reveals them to be composed of thousands of separate icy ringlets.
E) Though composed of thousands of separate icy ringlets if viewed up close, the main rings of Saturn may appear smooth and continuous when they are viewed from a distance.


OA is D

I think it is more to do with meaning.
Rest of the options suggests, whey Saturn's main rings are viewed closely, they are composed of thousands of separate icy ringlets. Instead D suggests Closer viewing reveals them to be composed of .....