ตู้รถไฟไอน้ำสร้างมากที่สุดในปีไหน ?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
in which year were the most steam locomotives built ?It is not neccessary to use all the tables.
 table_204_30:  id [ number]  "gauge" [ text]  "name" [ text]  "notes" [ text] 
SELECT "year built" FROM table_204_30 GROUP BY ("year built") ORDER BY COUNT(*) DESC LIMIT 1