We believe there are two reason for this phenomenon: the first is that the QUESTION samples in the training set are not sufficient; the second, which we consider as the more crucial one, is that the sample we apply, a 5-word sequence, does not cover the sentence beginning, where the typical question pattern locates, such as "what do you ..." or "how can I ...".
the incompetence of proposed model in detecting question mark is understandable, also still disappointing.