I have no idea how many I should know before the exam. I'm the kind of person who needs to learn off phrases for answers i cant just make them up. Also could you tell me which ones ye are learning off??
What i am doing is learning off the main topics like drugs,pollution, health,alcohol,environment,stress etc so i will have special vocab for those topics. Then im learning general vocab so i can write on any topic. Usually you need to talk about a problem and you have to give a solution to resolve it.