Task: Question Generation
Input (English): Context : Ludwik Gross (September 11, 1904 -- July 19, 1999) was a Polish-American virologist who discovered two different tumor viruses, murine leukemia virus and mouse polyomavirus, capable of causing cancers in laboratory mice. 
Subject : Ludwik Gross 
Relation : occupation
Output (English): What was Ludwik Gross's occupation?