Sorry, I'm too lazy to provide code samples.

The question is ambiguous. Of course, everything you can do in Perl, you can do in C, because perl is implemented in C. And everything you can do in C, you can do in assembler.

The real question, IMO, is whether you can express things in a "natural" and efficient way in a language. I think any declarative language such as Prolog or SQL is full of examples of things that are trivial to do in those languages, but awkward and inefficient in Perl. Of course, you can use SQL and Prolog from Perl if you want...

Another case is when you need speed and memory efficiency. Can you multiply large matrices in Perl efficiently? Not really, unless you use PDL or some other numeric extension, which happens to be implemented in C (there might be some in Fortran as well).