For configuring meal selections during a reservation, the most suitable field type to recommend would be (c) option set.
Option sets are used when there is a predefined list of options to choose from. In this case, for meal selections, there would likely be a set of predefined meal options available for users to choose from. The option set field type allows users to select one option from the list.
Global option sets (a) are similar to option sets, but they are designed to be shared across multiple entities. If the meal options need to be shared and used in different contexts, a global option set can be considered.
Lookup fields (b) are used to establish relationships between entities and may not be the most suitable choice for configuring meal selections, as they are typically used for linking to records rather than selecting options.
Two options (d) fields are used when there are only two possible choices, typically representing a true/false or yes/no scenario. It may not be the best fit for offering a range of meal options.
Therefore, the recommended field type for configuring meal selections during a reservation is (c) option set.