In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

[Q]: What do you need in addition to the LaserDisc in order to experience surround sound?, Context: Only one 5.1 surround sound option exists on a given LaserDisc (either Dolby Digital or DTS), so if surround sound is desired, the disc must be matched to the capabilities of the playback equipment (LD Player and Receiver/Decoder) by the purchaser. A fully capable LaserDisc playback system includes a newer LaserDisc player that is capable of playing digital tracks, has a digital optical output for digital PCM and DTS audio, is aware of AC-3 audio tracks, and has an AC-3 coaxial output; an external or internal AC-3 RF demodulator and AC-3 decoder; and a DTS decoder. Many 1990s A/V receivers combine the AC-3 decoder and DTS decoder logic, but an integrated AC-3 demodulator is rare both in LaserDisc players and in later A/V receivers.
[A]: playback equipment


[Q]: Why did Grand Duchy of Lithuania become a famous place for noble Ruthenian families to get intermarried?, Context: In Ruthenia the nobility gradually gravitated its loyalty towards the multicultural and multilingual Grand Duchy of Lithuania after the principalities of Halych and Volhynia became a part of it. Many noble Ruthenian families intermarried with Lithuanian ones.
[A]: after the principalities of Halych and Volhynia became a part of it


[Q]: What similar item to a GPS is mentioned here?, Context: The BeiDou Navigation Satellite System (BDS, simplified Chinese: 北斗卫星导航系统; traditional Chinese: 北斗衛星導航系統; pinyin: Běidǒu wèixīng dǎoháng xìtǒng) is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, and a full-scale global navigation system that is currently under construction.
[A]:
Chinese satellite navigation system