EntityCollection result = proxy.RetrieveMultiple(expression);
foreach (var entity in result.Entities)
{
  String output = String.Empty;
  if (entity.Attributes.Contains("account"))
    output = entity.Attributes["account"].ToString();
}

foreach (Entity entity in result.Entities)
{
    foreach (KeyValuePair<String, Object> attribute in entity.Attributes)
    {
        Console.WriteLine(attribute.Key + ": " + attribute.Value);
    }
}