C# If condition with values check

I'm looking for short coding style for the if condition containing multiple expression.

Let's suppose, I want to add if condition in a string variable name str. Here is my if condition.

if(str == "a" || str == "b" || str == "c" || str == "d")

I want to make this if condition short something like that.

if(str == "a" || "b" || "c" || "d")

I don't have to put str == again and again.

I know, I can do this using multiple ways:

• Using switch statement
• Making array/list of string and use LINQ or Contains to check.

I want to do some something similar to if(str == "a" || "b" || "c" || "d")

Thank you for your help!