In this work we used the knowledge based features in our previous work <cite>(Zhu and Lan, 2013)</cite> , which include four word similarity metrics based on WordNet: Path similarity (Banea et al., 2012) , WUP similarity (Wu and Palmer, 1994) , LCH similarity (Leacock and Chodorow, 1998) and Lin similarity (Lin, 1998) .