CREATE TABLE table_name_19 (round VARCHAR2, opponent VARCHAR2, venue VARCHAR2)

what round saw wakefield trinity wildcats u21 as the opponenet at belle vue?
SELECT round FROM table_name_19 WHERE opponent = "wakefield trinity wildcats u21" AND venue = "belle vue"
SELECT "round" FROM "table_name_19" WHERE "belle vue" = "venue" AND "opponent" = "wakefield trinity wildcats u21"