Answer:
A. are the sun, the sand, and the restaurants.
Explanation:
In the given sentence, the use of the words "also" and "as well" together in a sentence is faulty use of grammar. In the original sentence, the parallelism in the sentence structure makes it a correct and complete sentence of its own, thereby invalidating the use of the words "also" and "as well".
So, if these two grammatical errors are removed, then the sentence will become
"The best things about vacationing in the Caribbean are the sun, the sand, and the restaurants."
Thus, the correct answer is option A.
Option B is wrong in the use of the past tense "were".
Option C and D are wrong for their use of the words "too" and "also".