Table schema:
CREATE TABLE table_name_21 (class_to_1928 VARCHAR, year_s__of_manufacture VARCHAR, class_from_1928 VARCHAR)

Question: Which class to 1928 value had years of manufacture of 1921/23 and class from 1928 of BCi-21?
SQL: SELECT class_to_1928 FROM table_name_21 WHERE year_s__of_manufacture = "1921/23" AND class_from_1928 = "bci-21"