9. An apparatus comprising: a processor; and a memory coupled to the processor, wherein the memory comprises instructions which, when executed by the processor, cause the processor to: receive an input question for generation of an answer to the input question; generate a set of candidate answers for the input question based on an analysis of a corpus of information, wherein each candidate answer in the set of candidate answers corresponds to an evidence passage supporting the candidate answer as answering the input question; determine, based on the set of candidate answers, whether clarification of the input question is required; identify, in response to a determination that clarification of the input question is required, a differentiating factor in evidence passages of at least two candidate answers in the set of candidate answers; send, in response to a determination that clarification of the input question is required, a request for user input to clarify the input question, wherein the request for user input is generated based on the identified differentiating factor; receive user input from the computing device in response to the request; and select at least one candidate answer in the set of candidate answers as an answer for the input question based on the user input.
12. The apparatus of claim 9 , wherein the request for user input comprises a clarification question that is directed to the differentiating factor and a free-form text entry field into which a user may input a textual answer to the clarification question.