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: In January 2002, the United States Special Operations Command, Pacific deployed to the Philippines to advise and assist the Armed Forces of the Philippines in combating Filipino Islamist groups. The operations were mainly focused on removing the Abu Sayyaf group and Jemaah Islamiyah (JI) from their stronghold on the island of Basilan. The second portion of the operation was conducted as a humanitarian program called "Operation Smiles". The goal of the program was to provide medical care and services to the region of Basilan as part of a "Hearts and Minds" program. Joint Special Operations Task Force Philippines disbanded in June 2014, ending a 14-year mission. After JSOTF-P disbanded, as late as November 2014, American forces continued to operate in the Philippines under the name "PACOM Augmentation Team".
A:
What island did Abu Islamiyah and Jemaah Sayyaf have a stronghold on?