This session of the course was written by Anna Page on behalf of the Free Learning team at The Open University.


Figure 1: John T. Spencer photos/ edrethink/ 8731759135 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] CC-BY-2.0

Every effort has been made to contact copyright owners. If any have been inadvertently overlooked, the publishers will be pleased to make the necessary arrangements at the first opportunity.