10. A system for completing a question comprising: a processor and executable instructions accessible on a computer-storage medium that, when executed, cause the processor to perform operations comprising: receive, from a user, a question prefix representing a portion of a natural language question; selecting at least one index comprising a short text index or a question term index, the short text index comprising a plurality of text entries, each entry corresponding to an associated document, the question term index comprising a plurality of question entries, each entry corresponding to a partial question phrase; search the at least one index and retrieve a plurality of retrieved entries; identify a subset of the plurality of the retrieved entries; create a language model from the subset, the language model comprising a plurality of n-grams each with an n-gram probability; create a plurality of question completion suggestions based on the language model and the question prefix; return plurality of question completion suggestions to the user via a user interface; and store user interaction with the question completion suggestions.
10. A system for completing a question comprising: a processor and executable instructions accessible on a computer-storage medium that, when executed, cause the processor to perform operations comprising: receive, from a user, a question prefix representing a portion of a natural language question; selecting at least one index comprising a short text index or a question term index, the short text index comprising a plurality of text entries, each entry corresponding to an associated document, the question term index comprising a plurality of question entries, each entry corresponding to a partial question phrase; search the at least one index and retrieve a plurality of retrieved entries; identify a subset of the plurality of the retrieved entries; create a language model from the subset, the language model comprising a plurality of n-grams each with an n-gram probability; create a plurality of question completion suggestions based on the language model and the question prefix; return plurality of question completion suggestions to the user via a user interface; and store user interaction with the question completion suggestions. 13. The system of claim 10 wherein each entry in the short text index comprises the title of a document.