To simplify the problem, we convert a sentence with n errors into n sentences, each of which with only one error.
the following sentence, which contains three errors, ○ ○ E1 ○ ○ ○ ○ ○ ○ E2 ○ ○ ○ ○ E3 ○ will be converted to three sentences like: Chinese, a sentence is usually composed of several segments separated by comma "，".