If does not take the very big effort then to complete, may enter to the second stage: The uniform speed tours 10 minutes uninterruptedly, middle rests 3 minutes, altogether carries on 3 groups.

• 如果不费很大力气便完成，就可以进入到第二阶段：不间断地匀速地游10分钟，中间休息3分钟，一共进行3组。