针对以下C#代码,以下说法正确的是___ public class Teacher { public string teacherName = "Name_None"; public string teacherSubject = "Subject_None"; public Teacher(String name) { this.teacherName = name; } public Teacher(String subject) { this.teacherSubject = subject; } public Teacher(String name, String subject) { this.teacherName = name; this.teacherSubject = subject; } }