What is the output of the following code?

```
public class Test {
public static void main(String[] args) {
java.math.BigInteger x = new java.math.BigInteger("3");
java.math.BigInteger y = new java.math.BigInteger("7");
x.add(y);
System.out.println(x);
}
}
```
a. 3
b. 4
c. 10
d. 11

a. 3