注意事项:

1) 前提是开发者机器要装有Framework 3.5, 引入Reference : System.Core

2)  若发布服务器没装 Framework 3.5, 需手工把 System.Core.dll 加入到 bin 下再发布

=========================================== 

using System.Linq;

..

string[] list = new string[] { "mary", "tom", "david", "cathy", "tom" };    // 除数组外,  其它集合类也可 (如: List, Hashtable , Dictionary)
IEnumerable<string> result;

//
Console.WriteLine("--- 'FirstOrDefault' --");
result = Enumerable.Where<string>(list,
                 delegate(string item)
                 {
                     return item == "tom";
                 });
Console.WriteLine(Enumerable.FirstOrDefault(result));

//
Console.WriteLine("--- 'OrderBy' --");
result = Enumerable.OrderBy<string, string>(list,
                delegate(string item)
                {
                    return item;
                });
foreach (string str in result)
{
    Console.WriteLine(str);
}

//
Console.WriteLine("--- 'Min' --");
string result_str = Enumerable.Min<string, string>(list,
                 delegate(string item)
                 {
                     return item;
                 });
Console.WriteLine(result_str);

//
Console.WriteLine("--- 'Distinct' --");
result = Enumerable.Distinct<string>(list);
foreach (string str in result)
{
    Console.WriteLine(str);
}

//
Console.WriteLine("--- 'All' --");
bool result_bool = Enumerable.All<string>(list, delegate(string item)
                 {
                     return item.CompareTo("d") > 0;
                 });
Console.WriteLine(result_bool);

//
Console.WriteLine("--- 'Distinct' & 'OrderBy' & 'Where' --");
result = Enumerable.Distinct<string>(Enumerable.OrderBy<string, string>(Enumerable.Where<string>(list,
                delegate(string item)
                {
                    return item == "tom" || item == "david";
                }),
                delegate(string item)
                {
                    return item;
                }));
foreach (string str in result)
{
    Console.WriteLine(str);
}

===========================================

输出如下: 

--- 'FirstOrDefault' --
tom
--- 'OrderBy' --
cathy
david
mary
tom
tom
--- 'Min' --
cathy
--- 'Distinct' --
mary
tom
david
cathy
--- 'All' --
False
--- 'Distinct' & 'OrderBy' & 'Where' --
david
tom