Answer: The right answer is the C) "My grandmother made the following for Thanksgiving: turkey, stuffing, and potatoes."
Explanation: Just to elaborate a little bit on the answer, it can be added that colons are commonly used to introduce a list or a series, as in this example. The speaker is listing the dishes that his or her relative made for Thanksgiving, so a colon is placed preceding such list of items. The colon in options A and B are unnecessary, and the colon in option D should be replaced by a comma.