SQL - Conditional WHERE clause

Question

I have a SQL Server 2005 stored procedure that performs a query. This stored procedure takes in three parameters. The parameters are as follows:

@Stat

Answer 1

 c.StateID=@StateID 
 AND
 c.CountyID = ISNULL(@CountyID, c.CountyID)
 ...

Use IF statements

Or

 c.StateID=@StateID 
 AND
 @CountyID IS NULL OR c.CountyID = @CountyID)
 ....

Or dynamic SQL

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