Linq查询的问题，请教各位。

假如一个表有3列，line1,ine2,line3，
现在遇到一个情况是要根据前端用户的条件去选择shai'xuan哪一列，这个linq怎么写呢？
现在的做法是用switch 去判断：
switch(num){
case "1":
results = lines.Where(x=>x.line1.equals(...)).ToList();
break;
case "2":
results = lines.Where(x=>x.line2.equals(...)).ToList();
break;
...
}

请问有没有更好的方法呢？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;


namespace Q1080766
{
    class A
    {
        public string Line1 { get; set; }
        public string Line2 { get; set; }
        public string Line3 { get; set; }
    }
    class Program
    {
        static void Main(string[] args)
        {
            int num = 1;
            var p = Expression.Parameter(typeof(A), "p");
            var getp = Expression.MakeMemberAccess(p, typeof(A).GetProperty("Line" + num.ToString()));
            var body = Expression.Equal(getp, Expression.Constant("查询的值"));
            var lambda = Expression.Lambda<Func<A, bool>>(body, p);
            List<A> list = new List<A>();
            list.Add(new A { Line1 = "查询的值", Line2 = "", Line3 = "" });
            var query = list.AsQueryable().Where(lambda);
            foreach (var item in query)
                Console.WriteLine(item.Line1);
        }
    }
}

results = lines.Where(x=>
(num==1 && x.line1.equals(...))
|| (num==2 && x.line2.equals(...))
|| (num==3 && x.line3.equals(...))

).ToList();