Table: stanier_class_2_0
Columns: lms_1932_3_no
lms_1946_no
br_no
date_built
date_motor_gear_fitted
withdrawn

Question: When was the motor gear of the LMS 1946 no. 1901 model fitted?
SQL: SELECT "date_motor_gear_fitted" FROM stanier_class_2_0 WHERE "lms_1946_no" = 1901