听力原文： The Canadian police say that the new North American Free Trade Agreement which is to open frontiers across the continent has been exploited by drug smugglers from South America. The mafia can now move drugs across the continent with minimum supervision. Police estimate 60% of the cocaine which came through Canada this year has been brought through the east coast. Last year it was 10%. Police say the mafia are benefiting from the declining fishing industry. There are more boats available to move the drugs. The aim of the agreement is to ______.