10. 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 wherein identifying a differentiating factor in evidence passages of at least two candidate answers in the set of candidate answers comprises: identifying a plurality of differentiating factors between evidence passages of the at least two candidate answers; and selecting a subset of differentiating factors from the plurality of differentiating factors based on an evaluation of which differentiating factors in the plurality of differentiating factors clarify the input question.
10. 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 wherein identifying a differentiating factor in evidence passages of at least two candidate answers in the set of candidate answers comprises: identifying a plurality of differentiating factors between evidence passages of the at least two candidate answers; and selecting a subset of differentiating factors from the plurality of differentiating factors based on an evaluation of which differentiating factors in the plurality of differentiating factors clarify the input question. 13. The apparatus of claim 10 , 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.