Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_88 (class_from_1928 VARCHAR, class_to_1928 VARCHAR)

### Question ###
Which class from 1928 had a class to 1928 of BDi-21?

### Accurate SQL ###

SELECT class_from_1928 FROM table_name_88 WHERE class_to_1928 = "bdi-21"