Following (Serban et al., 2016;<cite> Elsahar et al., 2018)</cite> , we adopt some word-overlap based metrics (WBMs) for natural language generation including BLEU-4 (Papineni et al., 2002) , ROUGE L (Lin, 2004) and METEOR (Denkowski and Lavie, 2014) . To better evaluate generated questions, we run two further evaluations as follows.