Table: oldenburg_locomotives
Columns: class
railway_number_s
drg_number_s
quantity
year_s_of_manufacture
axle_arrangement

Question: Which Quantity has an Axle arrangement of 2′c h2?
SQL: SELECT AVG("quantity") FROM oldenburg_locomotives WHERE "axle_arrangement" = '2′c h2'

Question: Which Year(s) of manufacture has an Axle arrangement of 2′b n2?
SQL: SELECT "year_s_of_manufacture" FROM oldenburg_locomotives WHERE "axle_arrangement" = '2′b n2'