The effect of the earthquake that caused most of Port Royal to sink into the Caribbean was like the eruption that buried ancient Pompeii: in each case a slice of civilization was instantly frozen in time.
(A) The effect of the earthquake that caused most of Port Royal to sink into the Caribbean was
(B) As the result of an earthquake, most of Port Royal sank into the Caribbean; the effect was
(C) In its effects, the sinking of most of Port Royal into the Caribbean was the result of an earthquake
(D) The earthquake that caused most of Port Royal to sink into the Caribbean was, in its effects,
(E) Most of Port Royal sank into the Caribbean because of an earthquake, the effect of which was
On first galnce it appears that: Subject = The effect of earthquake and Verb = was like.
As we read further, we note that comparison is made between 'The effect of the earthquake that caused most of Port Royal to sink into the Caribbean'
and 'the eruption that buried ancient Pompeii'. But equal entities are not compared. Either the natural calamities must be compared or their effects must be compared.
Since 'the eruption that buried ancient Pompeii' is NOT underlined, we learn that the calamities need to be compared. Therefore, the Subject should be 'the earthquake' and not 'the effects of earthquake'.
Option D correctly compares earthquake and eruption using a grammatically correct sentence.