Even astronomers were amazed at the success of the Neptune flyby, which produced a photograph of a previously undetected moon;
this is likely to result in increased governmental support for the hitherto neglected U.S. space program.
(A) this is likely to result in
Since 'this' is preceded by ';' , it should be an independent clause ,but 'this' is a pronoun and it is ambiguously referring to more than one element in the preceding clause.
(B) that will cause
similar to explanation above it should an independent clause and 'that' is ambiguously referring to more than one element in the preceding clause.
(C) and which is likely to result in
Since ';' is not in underline portion ,it doesn't require usage of any connector(FANBOYS) to connect the independent clauses.
(D) this success is likely to result in
seems good because it clearly indicates the element which is being referred in the independent clause
(E) it is likely to result with[/quote]
'It' again ambiguously refers to more than one element in the preceding clause.