public static void BalanceTest()
{
var testA = new BankA();
var testB = new BankB();
var testC = new BankC();
testA.GetBalance();
testB.GetBalance();
testC.GetBalance();
}
static void Main(string[] args)
{
BankA a = new BankA();
Console.WriteLine(a.GetBalance());
BankB b = new BankB();
Console.WriteLine(b.GetBalance());
BankC c = new BankC();
Console.WriteLine(c.GetBalance());
}