Setting up putonghua as a standard language in education may do harm to the survival of some local dialects, a. but it is worthwhile to do so. (A. letter A; B Letter B; C. Letter C; D. Letter D) b. and so we have to be very cautious. (A. letter A; B Letter B; C. Letter C; D. Letter D) c. because this will endanger subcultures related to dialects. (A. letter A; B Letter B; C. Letter C; D. Letter D) d. but the harm will not be serious. (A. letter A; B Letter B; C. Letter C; D. Letter D)