单选题：Given code below:

Given code below:
```Java
Set s = new HashSet();
s.add(new Integer(1));
s.add(new Integer(2));
s.add(new Integer(1));
```
Which statement below is correct? @[A](2)

A. It compiles, but only two elements left in s.
B. It does not compile.
C. It compiles but exception raises at line 4, for 1 is already in the set.
D. It complies and there are three elements in s.





A.It compiles, but only two elements left in s.
B.It does not compile.
C.It compiles but exception raises at line 4, for 1 is already in the set.
D.It complies and there are three elements in s.


答案：A