Task: Question Generation
Input (English): Passage: On 21 September, 2015, Canadians Robert Hall and John Ridsdel, as well as Norwegian Kjartan Sekkingstad, and  Marites Flor; a Filipino woman, were abducted on Samai island near Davao. Ridsdel was beheaded by Abu Sayyaf on 25 April 2016 following a ransom deadline. ASG reportedly demanded more than $8.1 million for Ridsdel and the others. On 3 May, 2016, a video of the Ridsdel execution was released, along with new demands for the remaining hostages. A masked captor said, "Note to the Philippine government and to the Canadian government: The lesson is clear. John Ridsdel has been beheaded. Now there are three remaining captives here. If you procrastinate once again the negotiations, we will behead this all anytime". On 15 May, Hall  appeared in a new video, announcing that he and Norwegian Kjartan Sekkingstad would be decapitated at 3pm on Monday 13 June absent a ransom of $16 million. Both hostages wore orange coveralls, similar to hostages in videos produced by ISIL, to which Abu Sayyaf had previously pledged allegiance. The deadline passed. Hall was beheaded. On 24 June, Abu Sayyaf released Filipina Marites Flor. She was subsequently flown to Davao to meet President-elect Rodrigo Duterte. Duterte said he directed negotiations with the Abu Sayyaf. He did not elaborate. On 17 September, 2016, remaining hostage Norwegian Kjartan Sekkingstad was released on Jolo island. Abu Ramie, an ASG spokesman, claimed $638,000 was paid as ransom.
Output (English): How many months after his abduction was Ridsdel killed?