CREATE TABLE table_41370 ("Party" TEXT, "Marplan" TEXT, "Gallup" TEXT, "National Opinion Polls  ( NOP ) " TEXT, "Opinion Research Centre  ( OPC ) " TEXT, "Harris" TEXT)

What is Opinion Research Centre (OPC), when Party is Conservative?
SELECT "Opinion Research Centre (OPC)" FROM table_41370 WHERE "Party" = 'conservative'
SELECT "Opinion Research Centre (OPC)" FROM "table_41370" WHERE "Party" = 'conservative'