SAT Question 772835db: Form Structure And Sense answer and explanation

English - Form Structure And Sense - Subject Modifier Placement
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Most of the ice found on Earth is ice Ih, distinguished by a crystalline structure in which molecules form a hexagonal pattern. Amorphous ice, on the other hand, constitutes most of the ice in the ultrafrigid environment of outer space. Defined by a disorganized molecular structure, ______
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Difficulty:Hard
Which choice completes the text so that it conforms to the conventions of Standard English?