What are the shipping methods for the orders on 12/31/1994?
shipping method refers to l_shipmode; order on 12/31/1994 refers to o_orderdate = '1994-12-31'
SELECT DISTINCT T2.l_shipmode FROM orders AS T1 INNER JOIN lineitem AS T2 ON T1.o_orderkey = T2.l_orderkey WHERE T1.o_orderdate = '1994-12-31'