Answer: the correct one is E .systems; for example, hurricanes could be prevented from forming by artificial "reefs" of precisely shaped marine platforms
Step-by-step explanation:
(A) The portion after the semi-colon (for instance, ... platforms) is not a complete sentence.
(B) The portion after the semi-colon (for example, ... forming) is not a complete sentence.
(C) Which ... "reefs" ... prevent forming is unidiomatic; from is needed between prevent and forming. Prevent appears in the present tense, illogically implying that the artificial reefs—which don't yet exist, according to the earlier part of the sentence—already prevent the formation of hurricanes.
(D) The construction such as artificial "reefs" illogically implies that artificial reefs are weather systems. Additionally, the use of can in the present tense (as opposed to could) illogically implies that the artificial reefs—which don't yet exist, according to the earlier part of the sentence—do already exist.
(E) CORRECT. The semicolon is properly used to separate two complete sentences. Could is correctly used to describe a hypothetical consequence.