Q: This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
Passage: BSkyB utilises the VideoGuard pay-TV scrambling system owned by NDS, a Cisco Systems company. There are tight controls over use of VideoGuard decoders; they are not available as stand-alone DVB CAMs (conditional-access modules). BSkyB has design authority over all digital satellite receivers capable of receiving their service. The receivers, though designed and built by different manufacturers, must conform to the same user interface look-and-feel as all the others. This extends to the Personal video recorder (PVR) offering (branded Sky+).
A:
What is the name of the TV scrambling system BSkyB couldn't use?