As for the types and characteristics of errors made by the students, it could be analyzed for the causes of errors that most of the errors were influenced by intralingual interference: overgeneralization, ignorance of the rule restrictions, and incomplete application of rules (Richards & Sampson, 1994). Moreover, language transfer of the mother tongue (Thai) (Selinker, 1972; Richards & Sampson, 1974) also affected the numbers of errors found in this study, especially omission of words and misordering of words and sentences because of