& 30.9 & 22.82 & 17.55\
Capturing Greater Context [@tuan2019capturing] & 46.60 & **31.94** & 23.44 & 17.76\
Natural QG with RL based Graph-to-Sequence [@chen2019natural] & - & - & - & 17.94\
RefineNet [@nema2019let] & **47.27** & 31.88 & 23.65 & 18.16\
QPP&QAP [@zhang2019addressing] & - & - & - & 18.37\
ACS-QG$^*$ [@liu2020asking] & **52.30**$^*$ & **36.70**$^*$ & **28.00**$^*$ & 22.05\
UNILM$^*$ [@wang2020minilm] & - & - & - & 24.32\
ERNIE-GEN$^*$ [@xiao2020ernie] & - & - & - & 25.57\
UNILMv2$^*$ [@bao2020unilmv2] & - & - & - & 26.30\
ProphetNet$^*$ [@yan2020prophetnet] & - & - & - & **26.72**$^*$\
Syn-QG & 45.55 & 30.24 & **23.84** & **18.72**\

[| M[2.6cm]{} | L[3cm]{} | C[4cm]{} | R[2.7cm]{} | P[2cm]{} |]{} System & \#Questions Generated & Avg. \#Questions Per Sentence & Grammaticality & Relevance\
H&S & 381 & 3.81 & 3.49 & 4.23\
NQG & 100 & 1 & 3.48 & 3.28\
QPP&QAP & — & — & 3.9 & 4.03\
Syn-QG & 654 & **6.54** & **3.93** & **4.34**\

[| M[4.1cm]{} | L[3.4cm]{} | C[3.4cm]{} | R[3.4cm]{} |]{} System & Avg. novel unigrams & Avg. novel bigrams & Avg. novel trigrams\
H&S & 23.6 & 40.64 & 