As we cut our way through the original sentence, we can see that it's not actually grammatically a sentence. There are two independent clauses without a conjunction joining them. We'll look for this error in the other answer choices.

Choice (B) has the same problem. Choice (D) sets up an illogical comparison between "construction" in the answer choice and "countries" after the answer choice. Choices (C) and (E) are similar to each other. Their main difference is in the meaning conveyed; (C) conveys that Panama constructed the canal without Colombia, and (E) conveys that the two countries constructed it together. The sentence says that these two countries otherwise continued on similar courses, as indicated by the words "but other than." That means they didn't continue on similar courses with respect to the canal. Choice (E), therefore, doesn't fit the logic of the sentence.

The correct answer is (C).