C# 无奖竞猜：两行 Console.WriteLine 分别输出什么？

🏷️ C#

static void Main(string args)
{
    StringBuilder builder = new StringBuilder("world, ");

    AppendHello(builder);
    Console.WriteLine(builder.ToString());

    ClearBuilder(builder);
    Console.WriteLine(builder.ToString());

    Console.ReadLine();
}

static void AppendHello(StringBuilder builder)
{
    builder.Append("hello!");
}

static void ClearBuilder(StringBuilder builder)
{
    builder = null;
}

点击查看输出结果

world, hello!
world, hello!