So here the quesiton is looking for either 3 separate points, 1 per mark, or 2 points, 1 of which is a basic point and then 1 other point with added detail. This is a simple remember and regurgitate in the exam in the way the quesiton asks for. So oceanic crust is the tectonic plates found beneath the oceans, so has more weight acting on it than continental crust, so is denser, and thus in subduction zones is subducted beneath continental crust. That would be worth 2 marks because I've given a basic point and then given extra detail in addition. For another mark I would also state that oceanic crust is thinner than continental crust.