Before revision:  The dataset is freely available at our website for research purposes.abstract 
After revision:  The dataset is freely available at our website for research purposes.abstract \% by accuracy, which is 5.51\% higher than the best baseline model. We also measure human performance on our dataset and find that there is a big gap between machine-model and human performances. This indicates that significant progress can be made on this task. The dataset is freely available on our website for research purposes.