Because Miranda, the smallest moon of Uranus, has a large number of different surface features, including craters, mountains, valleys, and fractures, some astronomers suggest that at one time
repeated impacts broke the surface apart, and after which the fragments were subsequently rejoined because of mutual gravitational attraction.
(A) repeated impacts broke the surface apart, and after which the fragments were subsequently rejoined because of - - don't need 'and' if you use 'after which' (no need for 2 linking words/phrases); redundancy: 'after which' means the same thing as 'subsequently', so having both is fatal
'because of' is sketchy; it suggests indirect causation, while the clear meaning is that gravitational attraction was directly responsible
bad parallelism: first half is in active voice, but second half is in passive voice
(B) repeated impacts on the surface broke it apart, after which the fragments having rejoined with - - 'it' could potentially refer to either 'surface' or 'miranda' (or even 'uranus')
- 'having rejoined with' isn't a verb (an actual bona fide verb is required for parallelism)
(C) through repeated impacts that the surface broke apart, after which the fragments subsequently rejoined by - the wording suggests that the surface broke apart by itself (although perhaps because of the urging of the impacts) - doesn't have anywhere near as much directness as it should;
redundancy: 'after which' means the same thing as 'subsequently', so having both is fatal
(D) the surface broke apart with repeated impacts, after which the fragments having rejoined through - - 'with' is incorrect as it indicates an aspect of the breakage process itself whereas repeated impacts caused that process
- 'having rejoined': same problem as in choice b
(E) the surface broke apart as a result of repeated impacts, after which the fragments rejoined through - Correct ; proper parallelism: the surface broke apart is parallel to the fragments rejoined
Answer E
"preposition + WHICH" plays the same modifying role as does plain "which" -- namely, it modifies the noun preceding the comma.
in the original sentence, then, this "after which" doesn't make any sense, because there is no noun in the appropriate position (i.e., preceding the comma).
in the correct answer, "after which..." correctly modifies the immediately preceding noun "(repeated) impacts".