In the memory model of Atkinson and Shiffrin (as shown in Fig. 1), the memory process is divided into three parts: sensory memory, short-term memory and long-term memory. Sensory memory is immediate memory, which normally persists for only several seconds. Long-term memory is that which enables people to remember the rules of things. Short-term memory is the most important part of the entire memory process. It selects appropriate sections in the sensory memory to transfer to the long-term memory and will abandon other sections. However, as the most complex part in learning theory, memory is still a subject of debate. In this study, the working memory theory used to describe shortterm memory is accepted.