Answer: (iii) The development team in a controlled environment

Alpha testing is performed at the developer's site by the internal development/QA team (and sometimes a limited set of invited users) in a controlled environment, just before beta testing.

Why the others are wrong:

• (i) End-users — end users perform acceptance/user testing, or beta testing in real environments.
• (ii) A selected group of external users — that is beta testing (external users at their own sites).
• (iv) Automated testing tools — automated tools may support alpha testing, but alpha testing is defined by who runs it (the dev team in a controlled setting), not by tooling.

So alpha testing is typically performed by the development team in a controlled environment — option (iii).