Explanation

Creating a filter: In this question, the original sentence gets tied up coming out of the underlined portion. Two partial sentences have been stitched together into something that is not grammatically well-formed. "From" must lead to a noun, but the noun that follows it is meant to be the subject of the clause that follows, the clause with the verb "accumulate," and a clause cannot be as the object of a preposition. Since the "from" is the underlined part, we can must fix this problem by getting rid of the "from."

Applying the filter: our filter eliminates choices (A) and (E), since they have "from." Choice (B) looks clear and straightforward, so we can come back to it. In (C), the word "when" introduces a dependent clause that may only have a valid grammatical existence if it is followed by an independent clause, which it isn't. In other words, it starts something like, "When X, Y," but there is no clause "Y" afterward, so it's an incomplete sentence. Choice (D) turns "formed" into the beginning of a long modifying phrase, and as a result there is no proper verb or predicate corresponding to the subject "galaxies." We've eliminated all choices but one. The correct answer is (B).