Question: What is the Stack Exchange tag of the physics engine which is the software engine of Sonic the Hedgehog published on 2006-11-21?
Choices:
https://ja.stackoverflow.com/tags/perl
https://engineering.stackexchange.com/tags/mechanical-engineering
https://engineering.stackexchange.com/tags/industrial-engineering
https://stackoverflow.com/tags/ios
https://travel.stackexchange.com/tags/germany
https://security.stackexchange.com/tags/windows
https://stackoverflow.com/tags/havok
https://travel.stackexchange.com/tags/catalonia
https://superuser.com/tags/php
https://anime.stackexchange.com/tags/dragon-ball-series