Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.

Input: Consider Input: Context : The Ambushers is a novel by Donald Hamilton first published in 1963, continuing the exploits of assassin Matt Helm.
Answer : Matt Helm

Output: Which series is The Ambushers apart of?

Input: Consider Input: Context : Nikola Kalabic (until the start of World War II) worked in Land-registry management in Valjevo.
Answer : World War II

Output: In what war was Nikola Kalabic a combatant?

Input: Consider Input: Context : The Nelson Mandela 90th Birthday Tribute was held in Hyde Park, London on 27 June 2008 to commemorate Nelson Mandela's ninetieth birthday (18 July).
Answer : 27 June 2008
Output: The date of Nelson Mandela 90th Birthday Tribute was what?