To answer this question, we need to understand the concept of C# keywords. C# keywords are reserved words that have a specific meaning and cannot be used as identifiers (such as variable names or function names).
Let's go through each option to determine which one is not a C# keyword:
Option A) Implements - This option is incorrect because "implements" is a C# keyword. It is used when implementing an interface in a class.
Option B) public - This option is incorrect because "public" is a C# keyword. It is an access modifier that allows members to be accessed from outside the class.
Option C) delegate - This option is incorrect because "delegate" is a C# keyword. It is used to define a delegate, which is a type that represents references to methods with a specific parameter list and return type.
Option D) if - This option is incorrect because "if" is a C# keyword. It is used to perform conditional statements in C#.
Based on the explanations above, the correct answer is not provided in the given options. All options A, B, C, and D are C# keywords.