What makes a good question
From Physiki
For real-time formative assessment the instructor must be able to quickly understand student misconceptions from their InkSurvey submissions.
Multiple sentences are difficult for the instructor to process quickly so when using text input a one sentence answer to an open-format question is best.
Better yet, construct the open-format question so that it can be answered with an equation, figure, graph, or sketch. It is much easier and takes less time for you to process this type of information.