Which requirement applies to declaring an extension method in C#?
Correct answer A. It must be a static method in a non-generic static class, with this before the first parameter
Explanation
An extension method is a static method in a top-level, non-generic static class, whose first parameter is prefixed with this, as in public static int WordCount(this string s). It can then be called as if it were an instance method: text.WordCount(). It cannot access private members of the extended type. LINQ operators such as Where and Select are extension methods on IEnumerable.
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