单选题

以下代码的执行结果是？ public class Example { public static void main(String[] args) { TreeSet<String> t = new TreeSet<String>（ ）; if (t.add("one")) if (t.add("two")) if (t.add("three")) t.add("four"); for (String s : t) { System.out.print(s); } } }

Question

A. one

B. onethreetwo

C. onetwothreefour

D. fouronethreetwo