ans is B
beta testing -performed at client side by client under actual environment with actual data It is performed in Real Time Environment.
alpha testing -performed by client at developer site
Alpha testing is simulated or actual operational testing by potential users/customers or an independent test team at the developers' site. Alpha testing is often employed for off-the-shelf software as a form of internal acceptance testing, before the software goes to beta testing It is always performed in Virtual Environment.
refer
http://testingbasicinterviewquestions.blogspot.in/2015/03/best-difference-between-alpha-and-beta.html