Before revision:  We further make an investigation of several different c-TextGen techniques, and illustrate the advantages and disadvantages of commonly used neural network models . Finally, we discuss the open issues and promising research directions of c-TextGen .
After revision:  We further make an investigation of several different c-TextGen techniques, and illustrate the advantages and disadvantages of commonly used neural network models . Finally, we discuss the open issues and promising research directions of CTG .