Bunuel
In some cases, two clouds may break apart from the collapsing matter that typically forms a star, then holding each other in orbit around their common center of mass as a binary star.
A. star, then holding each other in orbit
B. star, and then holding each other in orbit
C. star and then hold each other in orbit
D. star and then hold each other, they orbit
E. star and then orbit, holding each other
Official Explanation
Creating a filter: in the original sentence, there's a problem with the conjunction. If one thing happens and then another thing happens, it's clearest to use the word "and." The participial phrase starting with "holding" would be more appropriate if the events were largely simultaneous and largely related. And "then" is not a conjunction.
Applying the filter: choices (B) and (E) have the same problem as (A) does. Choice (C) correctly and simply expresses the fact that one event comes after the other, using two verbs in a compound predicate. Choice (D) is not a sentence, since "they orbit" initiates a new independent clause without a conjunction.
The correct answer is (C).