C#

const int OPEN_EXISTING = 3;
const uint GENERIC_READ = 0x80000000;
const uint GENERIC_WRITE = 0x40000000;
const uint IOCTL_STORAGE_EJECT_MEDIA = 2967560;

[DllImport("kernel32")]
private static extern IntPtr CreateFile
    (string filename, uint desiredAccess,
     uint shareMode, IntPtr securityAttributes,
     int creationDisposition, int flagsAndAttributes,
     IntPtr templateFile);

[DllImport("kernel32")]
private static extern int DeviceIoControl
    (IntPtr deviceHandle, uint ioControlCode,
     IntPtr inBuffer, int inBufferSize,
     IntPtr outBuffer, int outBufferSize,
     ref int bytesReturned, IntPtr overlapped);

[DllImport("kernel32")]
private static extern int CloseHandle(IntPtr handle);

public static void EjectMedia(string computer, char driveLetter)
{
    string path = "\\\\" + computer + "\\" + driveLetter + ":";
    IntPtr handle = CreateFile(path, GENERIC_READ | GENERIC_WRITE, 0,
                               IntPtr.Zero, OPEN_EXISTING, 0,
                               IntPtr.Zero);
    if ((long)handle == -1)
    {
        throw new IOException("Unable to open drive " + driveLetter);
    }
    int dummy = 0;
    DeviceIoControl(handle, IOCTL_STORAGE_EJECT_MEDIA, IntPtr.Zero, 0,
                    IntPtr.Zero, 0, ref dummy, IntPtr.Zero);
    CloseHandle(handle);
}

For example,

namespace test
{
   using System;
   using System.Net;

   public class  classA
   {
       ...
   }
}