to swimwhy、？learn to do sth. 学着去做某事(在心里打算好了准备去学,还没有去)强调具体某次的动作.learn doing sth. 学习做某事(已经在学习了,现在进行时 ) 强调抽象的动作.那么应该填swimming?at the age of five 是一个时间点，所以应是某个具体动作。如：her mother said ding ziyin began learning to play the piano at the age of 10