Final answer:
A guest can order a dish of custard in three sizes: Single, Double, and Triple. The Belt Buster and Child size are not selectable options in this context. This type of question is common in middle school mathematics curriculum.
Step-by-step explanation:
When a guest orders a dish of custard, they may choose from the following sizes: a. Single, b. Double, and c. Triple. These are the three sizes available for ordering custard. The Belt Buster (5 scoops) and Child size (1/2 scoop) are not part of the choices given in the question and hence are not selectable options.
It's important to understand the context of this question, which might be related to problems involving choice combinations and basic arithmetic found typically in a middle school mathematics curriculum.
Additionally, if this question pertains to decision-making in a practical scenario, such as planning for a party or event, this would involve calculating the number of dishes based on the guests' preferences.