the answer is D. Some of the world’s highest waterfalls can be found in three countries: Venezuela, South Africa, and Peru.
a colon in a sentence means the auther can end the sentence with a period if he wanted and the sentence would still be correct.
in this case the sentence could be, "Some of the world’s highest waterfalls can be found in three countries."
this still looks and sounds correct and is a fully functioning sentence.
