Answer:
B: "The whole thing is made out of gelatin!" they exclaimed.
Step-by-step explanation:
The sentence in option B is punctuated correctly because what they exclaimed is in quotation marks and ends with an exclamation mark, which, in this case is taking the place of a comma. In a normal quotation, a comma should separate the words inside the quotation marks (including the comma) and the rest of the sentence.