Proficiency in input method skills is essential to improve typing efficiency, so typists should attend training courses that specialize in teaching Wubi input methods. Which of the following, if true, would most weaken the argument? ['Only typists who are proficient in input method skills have participated in training courses dedicated to Wubi input methods.', 'Only typists who have attended a Wubi input method training course can be proficient in input method skills.', 'Some typists are proficient in input method skills, but have never participated in a training course dedicated to Wubi input method.', 'Some institutions that teach other computer skills are more helpful for students to master input method skills than training courses that specialize in Wubi input methods.']