What happens after line 4 is run?

```

1 string s = “math is fun!”;
2 int f = s.at(0)
3 int t = s.size();
4 int n = s.at(5);
5 int y = s.at(s.5);
```

A. The value of y is space.
B. The value of y is i.
C. The program will not compile.
D. The program crashes when it runs.

B