C#.NET enums: which underlying datatype is <em>not</em> permitted for an enum?

Introduction / Context:
This question verifies your knowledge of which underlying types are valid for C#.NET enums. Picking an invalid type demonstrates understanding of the integral-only rule.

Given Data / Assumptions:

• Options include integral types and a floating-point type.
• Enums in C# require an underlying integral type.

Concept / Approach:
In C#, an enum's underlying type must be one of: byte, sbyte, short, ushort, int, uint, long, or ulong. Floating-point (float, double) and decimal are not allowed.

Step-by-Step Reasoning:

Verification / Alternative check:
Attempt enum E : float { A } in a test project; the compiler reports that the underlying type must be an integral type.

Why Other Options Are Wrong:
They list integral types that are explicitly allowed by the language specification.

Common Pitfalls:
Assuming any numeric type is acceptable or thinking that decimal/float work because they are “numbers.” Enums are intended to map names to discrete integral constants.

Final Answer:
float