<Li> Creativity, activity, service (CAS). CAS aims to provide students with opportunities for personal growth, self - reflection, intellectual, physical and creative challenges, and awareness of themselves as responsible members of their communities through participation in social or community work (service), athletics or other physical activities (activity), and creative activities (creativity). The guideline for the minimum amount of CAS activity over the two - year programme is approximately 3--4 hours per week, though "hour counting" is not encouraged . Previously, there was a requirement that 150 CAS hours be completed, but this was abolished in 2010 . However, some schools still require these hours . </Li> <Dl> <Dt> Subject groups </Dt> </Dl> <P> Students who pursue the IB diploma must take six subjects: one each from Groups 1--5, and either one from Group 6 or a permitted substitute from one of the other groups, as described below . Three or four subjects must be taken at Higher level (HL) and the rest at Standard level (SL). The IB recommends a minimum of 240 hours of instructional time for HL courses and 150 hours for SL courses . </P> <P> While the IB encourages students to pursue the full IB diploma, the "substantial workload require a great deal of commitment, organization, and initiative". Students may instead choose to register for one or more individual IB subjects, without the core requirements . Such students will not receive the full diploma . </P>

What does hl and sl mean in ib