The correct answer is C. The sentence should be completed with the words "the following", followed by a colon.
Colons are used to present explanation, draw attention to something (like to introduce an item or a series of items) or just to join ideas. In this case, we are introducing a list. The first part of the sentence informs the audience you will explain what they need to make a smoothie. Then, when you use the colon, it's like you're telling the readers "here are the items you need for your smoothie". It's not grammarly correct to use a comma to introduce a list.
Semicolons are used with clauses that could be separated sentences, therefore creating a longer sentence. The sentence above can't be separated into two different clauses because they would be missing something to make sense. We can use semicolons in a list at least one of the items in the list contain a comma.
