单项选择题

当执行下面代码时，会输出( )。
Boolean b1 = new Boolean(true);
Boolean b2 = new Boolean(true);
if (b1 == b2)
if (bi.equals(b2))
System. out.printin ("a");
else
System. out. println ("b");
else
if (bi.equals(b2))
System. out.println ("c");
else
System. out.printIn("d");