OK--since I'm bumping up against the 100 character limit, what's the preferred way to deal with line breaks in nested calls like this?

A:
```
r = find_nonrepresentable(cx, seen,
                          variant.args.iter()
                              .map(|aty| subst(cx, substs, *aty)));
```

B:
```
r = find_nonrepresentable(cx, seen, variant.args.iter().map(|aty|
                                        subst(cx, substs, *aty)));
```

C:
```
r = find_nonrepresentable(cx, seen,
                          variant.args.iter().map(|aty| subst(cx,
                                                              substs,
                                                              *aty)));
```

D: ...?