using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        //Renamed some of the variables to get clear understanding.

        List<string> expectedCategories = new List<string>(){"EXWORK", "CENTAGES", "PREMIUM"};

        List<Product> products = new List<Product>()

        {

            new Product("EXWORK", "ERECTION"),

            new Product("CENTAGES", "ERECTION"),

            new Product("PREMIUM", "SUPPLY")

        };

        var result = products

            .Where(x => x.CATAGORY == "ERECTION" && expectedCategories.Contains(x.PARTICULARS))

            .Select(x => x.PARTICULARS);

        Console.WriteLine(string.Join(", ", result));

    }

    public class Product

    {

        public string PARTICULARS{ get; set; }

        public string CATAGORY{ get; set; }

        public Product(string particulars, string category)

        {

            this.PARTICULARS = particulars;

            this.CATAGORY = category;

        }

    }

}