To solve this question, the user needs to know the expansion of the given abbreviations and cross-check if they are correct.

Now, let's go through each option and explain why it is right or wrong:

A. CTS - Common Type System: This expansion is correct. The Common Type System (CTS) is a component of the .NET framework that defines a set of rules that all .NET languages must follow.

B. CLS - Common Language Specification: This expansion is correct. The Common Language Specification (CLS) is a set of rules that defines a subset of the .NET framework that can be used by all .NET languages.

C. CAS - Component Authorization Specification: This expansion is incorrect. The correct expansion of CAS is Code Access Security. It is a feature of the .NET framework that provides security by restricting the code's access to resources and operations.

D. FCL - Framework Class Library: This expansion is correct. The Framework Class Library (FCL) is a collection of reusable classes, interfaces, and value types that are included in the .NET Framework.

Therefore, the answer is:

The Answer is: C. CAS - Component Authorization Specification